|Outreach N° 86 - Learning by Doing - Leaflets on Pressure and Water Technologies (OUTREACH - UNEP - WWF, 64 p.)|
LEAFLET NO. 39: YOUR COMMUNITY'S WATER SUPPLY
This leaflet brings together several school subject areas: geography, mathematics, science, and English. It encourages students to develop skills of observation, map-reading, data-collection and analysis, interviewing techniques, etc.
The project can involve as much as a yearlong commitment on the part of students if they are to complete the activity on community water supply needs, see notes below. In this case it may be necessary to introduce the topic at the start of the year, and then see what interest there is in pursuing the practical activity towards the end of the school year. If you wish to complete the topic in one session, then the activity suggestion could be modified accordingly.
A discussion about the water cycle, and on water sources that exist in your region might serve as an introduction to the leaflet.
The water-table or level of saturation
When the students are studying the diagram showing the water-table, point out to them that the water-table is not level. It tends to have high spots and low spots that match the valleys and hills of the earth's surface. It is usually arched under hills, but beneath plains it generally lies close to the surface. Oases, swamps and lakes can be found where the water-table is at the surface of the ground. Ask students what must happen to the water-table if rivers and lakes dry up after a long dry spell.
For more on water-tables, and the effect of wells on underground water supplies, see Learning-By-Doing Leaflet no. 42 SINKING WELLS.
Sources of water
To get accurate rainfall readings, make sure the diameter of the mouth of the funnel is the same as the diameter of the collecting jar. If the funnel mouth has a smaller diameter, the readings will be too small; if the mouth has a larger diameter, the readings will be too large. Help students find suitable locations for their rain gauges. Try to find open areas because locations sheltered by tree canopies, for example, will affect results. Ask the students to consider what other topographical features might affect the results. (You could, in fact, start the exercise by positioning the rain gauges in a variety of locations to see if the topographical features do dramatically affect rainwater collection.)
If daily rainfall is recorded for a long period of time, total rainfall may be divided by the appropriate number of days to determine the average weekly, monthly rainfalls. These results can be plotted on bar charts for further discussion.
When water drains into the ground
Ask students to think about when it rains really hard, and puddles form. Can they suggest which locations have puddles that take a long time to disappear? What kind of soil is found at these locations?
If possible, have the students collect samples that have high sand or high clay content. Have the students study the samples and describe the colour, texture, particle size of each soil before water is added. This may help them make predictions.
Soil samples may dry overnight, or they may take a few days to dry out. Wait until all the samples are dry. A speedier way to dry soils out is to heat them in an oven at a temperature of 105-120°C until they are thoroughly dry.
Discuss the results. Sandy soils are porous, composed of coarse particles with little organic matter, and tend to hold less water. When water soaks through sand and gravel, it can move downwards and sideways as fast as several metres a day. Crumbly, organic soils and sticky, clay soils are less porous and absorb more water. Water moving through clayey soils may move only at a rate of a centimetre or so every 24 hours.
To find out how much water each soil holds, first help students measure how much water drained out of each sample. To find out how much (approximately) stayed in each soil, subtract the amount that drained out from the amount they poured in.
Going further: The students should examine the water after it has drained through the soils. Is any of the water discoloured? Discuss with the students how substances can be washed through the soil as water drains. This presents a problem in the cases of chemical wastes and the leaching of nutrients valuable for plant growth. Students could repeat the exercise but mix some soil in the water before it is poured on the soil samples. They should examine the water after it has drained through the samples. Is it as dirty as before? The soils may have acted as a filter, helping to clean the water. Which soil proves to be the best filter?
ANSWERS TO QUESTIONS
What happens to rain?
1. Run-off on steep slopes is greater than on gentle slopes.
2. Evaporation in dry climates is greater than in humid climates.
3. Water percolates into sands more easily than into clay.
Try experiment 1 in Learning-By-Doing leaflet no. 8 SAVING SOIL ON A SLOPE to discover how the steepness of a slope affects the amount of surface run-off.
Collecting rainfall and surface run-off
Dams may be used to impound water from rivers and streams. Try to show students pictures of dams. Discuss the effects of building small and large dams upon the environment and local inhabitants. For more information on dams, see Learning-By-Doing Leaflet no. 41 BUILDING SMALL DAMS.
An individual household can collect rainwater that falls on the house roof. For more on this topic, see Learning-By-Doing Leaflet no. 40 CATCH A FALLING RAINDROP.
Activity: Your Community's Water Supply Needs
The students should be encouraged to record all data onto charts or diagrams. This activity is ideal for developing mapwork skills, whether it be studying topographical maps and geological maps (if they are available) or making scaled plans and maps of the locality. The students can also practice their surveying skills. Have students develop a list of questions to ask before actually beginning to interview people.
This project obviously demands a year-round commitment The project can be divided into two main study periods. At the beginning of the year, students could be introduced to the topic, and the initial data could be collected (including setting up rain gauges, drawing maps and doing initial surveys at water collection points). The second period of study, at the end of the year, could comprise problem identification and exploration of solutions. The intervening period would require the up-keep of the rainfall record and doing the community-wide survey. Solutions will vary depending upon the community need and the creativity of the students involved. For example, students might advocate behavioural changes on the part of water collectors, or construct water-collecting technologies that could supplement existing supplies.
LEAFLET NO. 40: CATCH A FALLING RAIN DROP
Introduce the topic by discussing water supply in your region. Students could first try the activities in the Learning-By-Doing Leaflet no. 39 YOUR COMMUNITY'S WATER SUPPLY.
If some households already collect water in drums, students may inspect the condition of the containers. Frequently, storage containers are rusty and leaking: the life of a well-constructed galvanised tank on a tropical island, for example, can be as short as two years because of the corrosive salty atmosphere.
(It is possible to use an old corrugated iron tank which has rusted through as the supporting frame for a ferrocement tank. The method is exactly the same as for constructing one with wire mesh. The tank must be brushed clean of rust and holes must be punched all over the tank. The tie wire is passed through these holes to fasten the inner layer of chicken wire to the outside.)
Water and Health issues
In discussing water catchment from rooftops, there are several water and health issues you may wish to raise. For example, students may talk about the health benefits of having water close by to the house.
Ask the students why a cover for the tank is necessary. It is to keep out mosquitoes. Without a cover, the stored water could become a breeding ground for these insects. Discuss what other measures should be taken to keep the stored water clean. Here are some suggestions:
* Clean your roof and gutter regularly;
* Make the gutters slope smoothly towards the tank. Sometimes there are bends and bumps in the gutters. Pools of water can collect there after the rains, and these provide a breeding ground for mosquitoes;
* Put wire mesh over the entrance pipe into the tank so that no insects can get into the tank;
* Make sure that there is a proper drain away from the drainage pipe, or make a concrete channel so that it is not always muddy around the tap.
Another issue concerns the type of roof used to collect the water. Galvanised iron, tiles or thatched shingles are suitable materials for roofs, but freshly-treated wooden shingles may contaminate the water with the treatment chemicals such as copper, chromium and arsenic, all of which are poisonous. Rainwater from thatched roofs tends to contain a lot of dirt and other suspended matter.
This leaflet helps students develop some mathematical skill and building skills such as carpentry, metalwork and plastering.
Mathematics: This topic on water tanks provides a practical application for the study of capacity (i.e. the amount of space inside a container, expressed in liquid measure, for example, litres) and volume (i.e. the amount of space taken up by an object, expressed in cubic feet/cubic metres etc.,). Students can estimate the capacity and volume of containers of various shapes and sizes as a prelude to this exercise. Set various problems for the students to solve. For example, what size tank would be needed to provide 100 students with 1 litre of water per day for a week?
Students can also practise describing circles using the string and nail technique shown in the leaflet. Construction of the tank involves more measurement work, including the mixing of ingredients to make concrete and construction of the roof frame. Constructing a scale model of a tank will give students practice in figuring out ratios.
Building skills: Students can practice the skills they will need to make a full-size tank by building their model tanks. Ideally, adults with the various building skills required should give the students demonstrations - and tips - before the students undertake the building of a full-size tank. These craftspeople may be prepared to supervise the work and lend specialised tools for this project.
Building a ferrocement cement water storage tank requires supplies of cement, steel wire mesh and corrugated galvanised metal sheets, as well as sand, water and sisal poles.
If through discussion and preliminary studies of the community's water supply, students determine that a storage tank would benefit the school/community, then supplies have to be acquired. Involve the students in the material collection process. The students may simply need to write letters to local industries asking for donated materials. Or, perhaps they will have to organise fund-raising activities. The students should form their own fund-raising committee and determine for themselves what action is necessary.
Depending upon the time and material resources available, this project may be simply one of tank construction or it may be expanded to include experiments on water-holding structures. Students should set hypotheses (e.g. round tanks are better than square tanks) and then set up experiments to test their hypotheses. Here are some suggestions:
Experimenting with different materials:
Students may construct small model tanks from different locally-available materials and devise means of comparing the tanks' water-retention capacities and their suitability for local climatic conditions. For example, students may build bamboo, not wire, ferrocement structures. Do the types of materials used limit the shape and size of the tank?
Experimenting with different shaped tanks:
Students may try out different shaped tanks. For example, do they find round ones work better than square ones? (Round ones are better to build than square ones. Square tanks need reinforcing at the comers which makes them more expensive.)
Experimenting with different consistencies of concrete:
Vary the mix of ingredients (sand, water, cement) to discover which mix can be applied the most easily; which proves to be the most water-proof, and which is strongest.
Developing Countries Farm Radio Network package no. 6 items 9A and 9B explain how to make a bamboo roof and eavestrough. These can be constructed for directing the rain water into the storage tank. Contact DCFRN, 595 Bay Street, 9th Floor, Toronto, Ontario M5G 2C3 Canada
For more information on storage tanks, see
Liklik Buk, a sourcebook for development workers in Papua New Guinea (1986) published by Liklik Buk Information Centre, ATDI, Unitech, P.M.B., Lae, Papua New Guinea
People's Workbook (1981) published by the Environment and Development Agency (EDA) Box 62054, Marshalltown, 2017 Johannesburg, South Africa
LEAFLET NO. 41: BUILDING SMALL DAMS
Uses of dams
Discuss why people build dams: for a water supply; for hydroelectric power; for irrigation. Use local examples to discuss the consequences of building dams. Consider the effect on people, land and wildlife upstream from the dam and downstream from the reservoir. Interview people living near a dam to find out their views on whether the dam should/should not have been built.
A dam for your community
Have students brainstorm benefits and disadvantages of building a new dam in your community. For example, some of the advantages could include a source of safe drinking water and water for irrigation year-round. Some of the disadvantages could include the spread of certain diseases, such as bilharzia and destruction of natural habitats. Which people would benefit most/least? The topic could be discussed in a class debate, with students voting on the issue.
How big is a dam?
The students can apply their mathematical knowledge of capacity and volume to a practical exercise where they work out how much water can be held by a dam on a nearby stream. Here's what they should do:
1. Select a site on the stream where a dam could be built.
2. Stretch a string across the place where the top of the dam wall would be. Hang another string from the middle of this string. This will show the height of the dam wall, see picture. It should be no higher than 2 metres, otherwise the dam can become dry or fill up with sand too quickly.
3. To find out how much water the dam will hold, use a spirit level or water level (see learning leaflet no. 37 UNDER PRESSURE) to find the place where the stream is level with the top of the wall. Measure the distance between this place and the dam wall. Then, the amount of water the dam will hold in cubic feet/metres is approximately 1/6 × this distance × the length of the wall x the height of the wall, see picture below:
ANSWERS TO QUESTIONS
Choosing a site
1. A narrow valley with steep banks on both sides. This will reduce the length of the dam wall or dike;
2. The stream-bed should have a gentle incline. A slow-running stream is less likely to cause excessive build-up of sand and silt.
3. The ground should be a clay-silt soil mixture that will hold water.
4. The reservoir area should be large enough to hold enough water but not too large. If it is too large, too much water will evaporate.
5. The storage site should be close to the users. It is better to build above a village than below it. Then, people will wash in the stream coming out of the dam, not in the stream going into the dam. This will help to keep the dam water clean. Another criterion is that materials for construction should be nearby. Materials required depends upon the type of dam to be built. Dams may be made from rocks, earth and concrete.
Preparing the site and building the wall
Earthen dams: If the wall was built on sand or silt, the water will slowly empty out from under the wall. A solid foundation is vital in order to prevent the collapse of the dam wall.
Collecting water from a dam
You may wish to discuss with students how water should be collected from a dam. The person collecting water from the reservoir itself is more likely to contaminate the supply. (For example, germs may enter the water from the water container.) To safeguard the water supply, a covered well may be dug behind the dam. A dam will raise the groundwater level closer to the surface. Therefore, the well would not have to be as deep. In the case of a concrete and stone dam, piping can collect water from the sand behind the dam wall, and channel it through the wall to a tap on the other side of the dam. The sand upstream from the dam stores the water and filters it as it travels to the pipe and through the dam. The water that comes out of the pipe is clean.
The water held by a dam can bring many benefits to a village, but it can also create problems if people are not aware of the dangers of waterborne diseases. Discuss such diseases with your students and explain how the spread of these diseases can be prevented. See learning leaflets on PURIFYING WATER. Animals and people can pollute the reservoir water by entering it to swim, bathe or wash their clothes and dishes. All of these activities pose possible health problems to others who drink water from the reservoir.
LEAFLET NO. 42: SINKING WELLS
This leaflet is concerned with ways of recovering water from underground. People who live in lands where there is little surface water in the form of rivers and lakes have to find and use the reservoirs of water held underground. Such people know that there may be water close to the surface near a dry river bed or hollow in the land which contains water only a few hours or days during the rainy season. The type of vegetation growing is another indication that there may be water underground. Many people dig, by hand, 50 or 60 metres before finding water. Mechanical drills can obviously do the job much quicker, but they are more expensive.
This leaflet encourages students to consider factors that might influence the siting and type of wells required. Students develop skills in comprehension and logic.
Collecting water underground
This experiment can be used to show students what a water-bearing strata looks like, what the water-table is, and how pumps draw water up from underground. Water-bearing strata is usually sandy soil surrounded by impermeable rock.
ANSWERS TO QUESTIONS
How deep should a well be?
Wells which are sunk far below the permanent water-table (wells A and C) should have a constant supply of water because there is water all the time. Well B has been sunk into the zone of intermittent saturation (see Learning-By-Doing Leaflet no. 39 YOUR COMMUNITY'S WATER SUPPLY). This well will have water after rains have fallen, but will go dry in periods of drought when the water-table falls. If a well does not reach the water-table (well D), it will be dry.
Where to sink a well
1. Digging wells near rivers or lakes may seem strange if river or lake water is available. But soil acts as a filter, and well water is usually cleaner, and more free of bacteria than river or lake water. A well may also provide water during the dry season when the water-table has fallen and the nearby river has dried up.
2. Ground water, being a liquid, gathers in low areas. So the lowest ground, say a valley, is generally the best place to dig or drill a well.
3. Some types of rock can hold a lot of ground water, and some hold no water at all. If a well is sunk into gravel or sand, you may draw all the water you need (well 1). Wells sunk into a layer of clay (well 2) will be dry because the ground water soaks through clay very, very slowly. (If well 2 were dug deeper, it would not be dry.) Hard impermeable rocks such as shale or granite cannot hold ground water at all, so well 3 would be dry.
4. Sometimes ground water has impurities that move with it. For example, harmful wastes from a latrine may get into ground water, and stay with it as the water trickles through the ground, and seeps into wells. (Another example is saline water from oceans getting into wells that are located near oceans.) A well should be uphill from a latrine and be some distance (65 feet/20 metres) away from it. Well 2 is likely to provide safer water than well 1.
Types of well
1. a driven well
2. a drilled well
3. a dug well
Artesian wells You might want to explain artesian wells to your students. This is one type of well in which water reaches nearly to the surface of the ground. It may even spout up into the air like a fountain!
To understand how an artesian well works, there are several things to realise. The first thing is that aquifers do not always lie flat below the surface of the ground. They may be slanted, or inclined. Second, aquifers may also be sandwiched with a solid layer of rock above and below it. This is a confined aquifer. (An unconfined aquifer is one which is not sandwiched between solid layers of rocks.) If an inclined 'sandwiched' aquifer occurs, then an artesian well may be sunk, see diagram below.
An artesian well is always located 'downhill' from the top of an inclined aquifer. This means that the well taps part of the aquifer that is lower than the aquifer's upper end. Since water seeks its own level, the pressure from the water in the upper end of the aquifer forces water up the well hole, see learning leaflet no. 38 GETTING LIQUIDS TO WORK FOR YOU. Because the aquifer is surrounded by solid rock, water cannot move from the aquifer except up through the well. If the pressure of the water is great, water may spout up out of the well like a fountain.
Artesian wells will stay full if the ground water supply is recharged by rainfall in the area at the upper end of the aquifer.
When a confined aquifer has the form of a syncline (said: SIN-kline) (i.e dipping towards a certain point), an Artesian basin results. Rain water enters the permeable layer at its exposed end(s). This layer becomes saturated with water. The Sahara Desert is underlain by an extensive artesian basin. The diagram at right shows a section of it.
In places, the aquifer bends up towards the surface, and wind erosion sometimes exposes it. When this happens, pools of water occur and these are called oases. If the aquifer is near to the surface, wells can be - and are often -sunk.
For more information on ground water, see OUTREACH issue no. 6.
For more information on methods of raising water from wells, see Learning-By-Doing Leaflets on WATER-LIFTING DEVICES.
PART OF THE ARTESIAN BASIN OF THE SAHARA DESERT
LEAFLET NO. 43: WATER-LIFTING DEVICES (1) USING SIMPLE MACHINES
Before students begin these activities, make sure they have completed the series of learning leaflets on simple machines so that they can apply the mechanics principles they have learned.
Invite the students to compare all the water-lifting devices illustrated in the student leaflet. Which do they think is the easiest to make? (Consider availability and cost of materials, labour resources and skill required). Which do they think is easiest to operate? Which raises water the fastest? The slowest? Which uses the cheapest, most reliable equipment that is easy to maintain? Which method is the best, in their view, for raising drinking water? Why? Which is the best method for raising water for a large population? Which method is the best for raising irrigation water? Why? Students should also consider health factors such as prevention of water contamination.
When students try designing their own water-lifting machines, encourage them to make models of the machines. Have they considered why the water is being raised, how much and how high it needs to be raised, what materials are locally-available?
ANSWERS TO QUESTIONS
The diagram below indicates where the load, effort and fulcrum are on a shaduf:
Bucket and windlass
The answer is 300 litres. The bucket pump will serve a limited number of people: ideally this should be between 30 and 60 individuals.
Where large numbers of people or cattle require water, or where water is required for irrigation, then the water delivery rate is inadequate. The bucket pump is primarily designed for providing water for domestic use only.
The Persian wheel lifts water faster than the shaduf, and it doesn't require such hard work. While it doesn't work as fast as a diesel or electric pump, it can be made and repaired by local craftspeople using locally-available materials. It is an example of both an appropriate technology and an intermediate technology.
The rope-washer pump
The picture shows one of the pumps for garden irrigation that was developed under a research project funded by the Overseas Development Administration (U.K.) and based at Loughborough University of Technology in England and the University of Zimbabwe.
This simple pump is based upon a very old principle having been used in Roman times, but it has been adapted to use materials which are now widely available and cheap. For example, in Zimbabwe, with all the materials bought at shop prices, the cost of the material amounts to about Z$70.00 (about UK £15.00). Some farmers have made the pump for less than Z$20.00 (UK£4.00) by using materials on their own.
How it works: The pump consists of a continuous rope, with rubber washers attached, which is pulled up through a pipe by means of a pulley-wheel. The rubber washers are slightly bigger than the inside of the pipe. When the bottom of the pipe is inserted in water, the rubber washers, moving upwards, draw water with them. As they emerge at the top of the pipe, the water falls into a collecting tank. An old 200 litre drum is ideal as a tank. The water must then be taken to the crops. Plastic hose piping is a very effective way of doing this.
What materials are needed: Pipe, rope and an old tyre are the most important materials. Where available, strong PVC pipe is ideal. Steel pipe may also be used. If piping is unavailable, then a square pipe may be made from wooden boards. Strong water-resistant rope, such as nylon braid, is the best, although ropes made of sisal, manila or even strips of car tyre may be used. Steel bars, strip of inner tube, some poles, wire and nails are also required.
Tools needed are a sharp knife, a hammer, a pair of pliers, a wood-saw and wood chisel and a hack-saw. Basic welding facilities can improve the quality of the handle. An experienced pump-maker, with all the materials ready, can make and install the pump in one day.
The rope-washer pump can:
* lift water from open waterholes, hand-dug wells and streams but not from narrow machine-drilled boreholes.
* pump water quickly when water is near the surface.
* lift water from deep wells. Water has been lifted from depths of more than 20 metres. However, in deeper wells, water flows from the pump more slowly because it is harder to work. A variation of the rope-washer pump is shown in the picture at right. This pump is used in Peru.
* lift water into overhead tanks.
* be operated by one or two people at a time.
* cope easily with mud, weeds, etc.
* be easily understood and repaired by the farmer when something goes wrong.
* it saves time. To irrigate a garden of 0.1 hectares (a little over 30m × 30m) using a rope-washer pump (if pumping up water from a 5 -deep well) would take about 6 hours per week, or a little over an hour a day. To water the same sized garden using a watering-can would take at least 4 hours each day.
In order to make this technology widely available, good training is required. A detailed manual has been published in English, on the construction of the rope-washer pump. A 20-minute video (with no narrative) is also available showing the main steps in making the pump. The manual and video are available from Intermediate Technology Publications, 103 Southampton Row, London, WC1 4HH, UK. The manual costs £4.95 incl. air speed postage (£5.55 to the Far East and Australasia). The video costs £19.95 incl. postage (£22.25 to the Far East and Australasia). Training in the construction of the pump is only the first step. Training in garden irrigation for farmers, and in business methods for pump-makers, are also available. For further details of such courses and for additional information on the rope washer pump and other irrigation pumps, please write to: Robert Lambert, School of Development Studies, University of East Anglia, Norwich NR4 7TJ, UK
Source: "Technology for Garden Irrigation" by Robert Lambert, Footsteps (No. 7 June 1991) -Footsteps is a quarterly paper published by the Tear Fund, linking health and development workers worldwide.
The spiral is a screw shape. Above is a diagram showing an archimedean screw being driven by a foot-powered pump from a bicycle frame with standard pedals. Perhaps, the students can devise another way of powering an archimedean screw.
LEAFLET NO. 44: WATER-LIFTING DEVICES (2) SIPHONS
How does the siphon work? Gravity pulls the water down on the lower side of the tube. At the same time, air pressure pushes the water through on the higher side. Together, they create the flow of water through the siphon. When the water is at the same level in both jars, gravity is exerting the same pull on both sides of the tube and the flow stops. Why does the tube have to be full of water first for the experiment to work? Try the experiment without the tube full of water. When it has air only in it, water is prevented from rising to the top of the high side. You can start a siphon working by putting one end in the jar of water, then sucking on the other end of the tubing until the water is almost all the way through the tube. Take the tube quickly out of your mouth and hold it, pointing down, at any point lower than the level of water in the full jar. As long as the free end of the tubing is lower than the water level in the jar, water will continue to drain. You could experiment with tubing of different lengths, too.
You can extend the work using the siphon bottle by doing the following with your students:
* With the siphon bottle, instead of blowing hard to move water up, try making devices that when squeezed, will push the water out of the bottle for you. Try a blown-up balloon or a bicycle pump. In the case of the latter, don't pump too hard: the siphon bottle could break. Ask the students what these devices resemble. (e.g. a fire extinguisher).
* See if heating the water in the bottle affects the way the water behaves. The students can use their hands or place the siphon bottle in a bucket of very warm water. If the long tube is held upright, measure how far the water from the siphon bottle rises. This is like an air thermometer. This experiment explores what happens when air pressure in the bottle increases.
Hose and bucket pump
For more on hose and bucket pumps, read "Clean Water for Elemit - a letter from the village health worker" OUTREACH issue 73.
One of the disadvantages of the hose and bucket pump is that not all the water in the bucket inside the well can be discharged. There is always water in the pump that cannot be pumped out
A Siphon Bottle
Through the experiments, students will discover that water will flow from one container to another only when the air is being sucked out of the bottle or when the two water levels are different. In a closed container like the siphon bottle, air has to go out in order for water to come back into the bottle, and when water goes back out, air comes in.
ANSWERS TO QUESTIONS
Completing the paragraph: air; below; higher; downwards; same. Experiments: (3). There would be no water flow in (1) and (4) because the water levels are the same. In (2) the water would flow from jar A to jar B.
Hose and bucket pump
(1) It is important to convince the woman that there is no evil spirit at work - just gravity. The water is being sucked back into the hose as the bucket attached to the hose moves to a lower level. Let the woman feel that the hose "sucks" when the bucket is lowered: she would feel it quite distinctly if she put her finger just inside the hose. One way to make sure this doesn't happen is to fix the hose so it cannot be left in a collecting bucket.
(2) If the discharge outlet is plugged with a cork before lowering the bucket, the water in the hose won't run back into the bucket as it's lowered.
(3) Use a larger bucket, raise the support or use a more efficient windlass, perhaps one operated by a windmill.
Picture (a) shows water running into the bucket. (b) shows water being sucked back into the hose and bucket. (c) shows the hose bucket hasn't reached a level where the flow will take place yet.
Design a pump
The project may begin with a class discussion of existing water supplies: what is the rainfall in your region; where community members obtain their water over the course of the year (the source may vary depending upon the season); how adequate existing supplies are for meeting the needs of the local community; what the quality of the water supply is; what local residents know - and do - about preventing water supplies from becoming contaminated; even the taste preference of local water supplies (e.g. underground supplies may have a different taste and appearance to surface water.)
It is important to discuss your community situation with the students, because the choice of design depends upon local conditions:
* Consider what sources of energy are available. For example, would a wind pump be suitable? Are there draught animals (oxen, donkeys etc.) available?
* What materials are available - wood, clay, stones, straw, leather? Some industrial products such as oil drums, car tyres, buckets, gas pipes, plastic tubing may or may not be easy to obtain. What about cement, nuts and bolts, metals?
* Who can maintain the pump? Are there mechanics living in the community? Who should be responsible for the maintenance?
* Point out the cheapest pump is not necessarily the best pump, and the cleanest pump may not be the cheapest. Who will pay for the installation of the pump and its maintenance?
* How many people live in the community, and will use the pump? What uses will the water be put to? When in the day will most people use the pump? Are the water demands constant throughout the day/year?
Ask the students to examine the design criteria, and decide for themselves which are the most important, and which are the least important. (Priorities may be determined after class discussion, or after they have talked to members of the local community about their water needs.)
A useful publication for work on pumps is Water for Tanzania published in 1983 by The Physics Curriculum Development Group (PLON) in Holland for 14-15 year olds. This is an imaginative resource both for science and other subject areas. Photos and text give background to Tanzanian water problems and needs and show in detail (diagrams, photos) how different types of pumps work. It includes questions for activities and discussions. It is available for £3.60 from Centre for World Development Education, Regent's College, Inner Circle, Regent's Park, London NW1 4NS ENGLAND or the book may be ordered from NIB publishers, P.O. Box 144,3700 AC Zeist, THE NETHERLANDS.
LEAFLET NO. 45: WATER-LIFTING DEVICES (3) SUCTION PUMPS
Much of the information for this leaflet is adapted from: Water for Tanzania published in 1983 by The Physics Curriculum Development Group (PLON) in Holland for 14-15 year olds. This is an imaginative resource both for science and other subject areas. Photos and text give background to Tanzanian water problems and needs and show in detail (diagrams, photos) how different types of pumps work. It includes questions for activities and discussions. It is available for £3.60 from Centre for World Development Education, Regent's College, Inner Circle, Regent's Park, London NW1 4NS ENGLAND or the book may be ordered from NIB Publishers, P.O. Box 144, 3700 AC Zeist, The Netherlands.
Another useful resource is Messing Around with Water Pumps and Syphons: A Children's Museum Activity Book by Bernie Zubrowski, published in 1981 by Little, Brown and Company (ISBN 0-316-98877-4 (pbk.) This book encourages children to play around with water and common materials in order for them to begin to understand how liquids move from one point to another and how such things as pumps, fire extinguishers and air thermometers work.
How high can you pull up water?
The following diagrams provide further explanation of this experiment:
Galileo discovered how high water could be 'pulled up' when he tried to construct a pump to suck water out of a (...). Since the pump could only suck water about 20 feet and no further, he had to up three pumps in succession to pump the water all the way out of the mine.
You can expand this section to include work on barometers. If a mercury barometer is available, show it to your class. Measure the height of the mercury column supported by air pressure (76cm or 30 ins. at sea level). As mercury is 13.6 times as dense as water, get the students to calculate how high air pressure would force water up a vacuum tube (10.3m or 34 feet at sea level).
Making a suction pump
When making a suction pump, students may be able to use such things as marbles for valves; squeezable bottles instead of a balloon and funnel. In real-life suction pumps, PVC tubes are used: you could try these or hollow bamboo tubes. The piston could be made from corks, a flexible rubber flap cut from the inner tube of a bicycle tyre, and a pole. The flap must be placed into the tube with its edges curled upwards:
Here is a diagram of a suction pump, and a sketch of one made by some students:
ANSWERS TO QUESTIONS
How a suction pump works
The information below is taken from: Water for Tanzania by the Physics Curriculum Development Project (PLON), see above reference.
The order of the pictures should be:
1(a); 2(f); 3(c); 4(g); 5(b); 6(e); 7(d)
The students could create a poster showing the different stages in order, and then the class could discuss what's happens at each stage. The different stages are explained as follows. (Please note the handle has been omitted from the drawings. The diagrams indicate the air pressure at the various stages):
1. The piston and valve are above ground. Air is below the piston. The piston is at the highest position. The water level in the suction pipe is at the same level as the water in the well.
Figure 1 (a)
Figure 2 (f)
2. The piston is forced down. The pressure of air underneath the piston increases. The valve stays closed. The piston is prevented from being pressed down as far as the valve because of the air underneath. If the pressure is too high, the air pushes the flaps on the piston upwards and escapes upwards.
Figure 3 (c)
Figure 4 (g)
3. When the piston is raised to its highest point, the pressure of air trapped between the piston and the valve is less than the pressure of air in the rising main so the valve is pushed open. The air from the rising main flows into the cylinder. The pressure of air in the pump is less than the air pressing down on the water in the well, so the water is "sucked" up the rising main a little way.
4. When the piston descends again, the air pressure in the cylinder is increased, so the valve shuts. The water in the rising main stays at the same level and air is forced out of the cylinder past the piston. This is repeated, with the result that the water in the rising main rises higher with each stroke.
Figure 5 (b)
Figure 6 (e)
Figure 7 (d)
5. After several strokes of the pump, the water rises so high that it passes the valve and enters the cylinder. The last of the air is forced out of the cylinder.
6. When the piston is pushed down again, water is forced past the flaps, and rises above the piston.
7. The water above the piston flows out of the pump when the piston is moved upwards. New water under the piston is sucked upwards through the valve by the pressure of the air on the water in the well. If pumping continues, water will continue to flow out of the discharge outlet - as long as the rising main stays under water.
Making your own suction water pump
In theory, a suction pump could raise a column of water 10.3 m (34') at sea level.
In practice, however, even the most efficient suction pump can create a negative pressure of only one atmosphere. Because of friction losses and the effect of temperature, a suction pump at sea level can actually lift water only 6.7m to 7.6m (22' to 25'). To explore more on the effect of altitude and water temperatures on the effectiveness of a suction pump, see Village Technology Handbook published by Volunteers in Technical Assistance (VITA) (revised edition printed 1970) 80 South Early St., Alexandria, Virginia 22304, USA.
The water seal might prevent air leaking when the piston is worn, but some drops of water will leak pass the flaps, and this water can contaminate the drinking supply.
LEAFLET NO. 46: WATER-LIFTING DEVICES (4) FORCE PUMP
ANSWERS TO QUESTIONS
How the displacement pump works
The questions posed are taken from Water for Tanzania:
1. Yes. The water begins to rise in the rising main. The higher it rises, the more difficult it becomes to force it further upwards. Greater effort is needed to pump, especially to push the handle up. The valve will begin to leak as the pressure of the water at the bottom of the rising main becomes greater, so that water will also be forced past the piston. The height to which water can be pumped is determined by the degree to which the valves leak.
2. The water wants to be at the same level, so raising the water takes work (force × distance). The higher the volume of water has to be lifted, the same volume of water thus is in the pipe. The weight of the water gets heavier the deeper the well, (not like a bucket in a well whose water has the same weight in deep wells as in shallow wells).
3. The weight of the water in the rising main places lots of strain on the piston rod.
4. Yes. Pressure is Force/Area. If force applied to the valve is the same, then the pressure on the smaller area of valve 2 in the narrow guide pipe is greater than the pressure applied to valve 1 in the wider rising main.
Lift pump versus force pump: Force pump -valve 1 should be open, and valve 2 should be closed. Lift pump - piston rod should be raised, and the valve should be open.
Here is an exercise that can help determine your students' understanding of how force and lift pumps work:
Lift pumps versus force pumps
Here are some statements that describe force pumps and/or lift pumps. Put a 'T' next to those statements that are true, and a 'F' next to those statements that are false:
1. With the lift pump, the pumping mechanism is located at the top of the well, and raises water by suction.
2. With the force pump, the pumping mechanism is placed at or near the water level, and pushes water up.
3. The force pump raises water on the upstroke, and the lift pump raises water on the downstroke.
4. The force pump relies on atmospheric pressure.
5. Most lift pumps raise water from shallow wells, while force pumps are generally used to raise water from deep wells or boreholes.
Answers: 1 T; 2T; 3 F; 4 F; 5 T.
LEAFLET NO. 47: PUMP PROBE AND PATROL
This leaflet can serve as a way of concluding work on pumps by inviting students to apply their newly-gained knowledge to practical work in their own community. Alternatively, the ideas in this leaflet may be used by students who do not have time for an in-depth look at the workings of pumps.
The leaflet attempts to make students realise that an acceptance of new technologies by a community depends upon more than people understanding the nuts and bolts of the technology. Cultural, social and health factors should also be considered. For example, there seems to be little doubt that the encouragement of community participation in a new technology pays off in many ways. Installations which are put in place with active community support are much more likely to survive than those in which villagers have neither been consulted nor involved.
This survey encourages the students to take part in a problem-solving activity: pump problems are identified, and students come up with creative solutions. Through this project, students can develop skills in observation, gathering data, prediction, communication, mapwork, and mathematics.
The data collected may be useful to the community at large. Through the survey, factors determining the success or failure of a community pump might be identified. The survey's results may also be beneficial to policy-makers at the national level who are concerned about introducing specific pump technologies. Perhaps, a national project could be established - a PUMP PARTICIPATION scheme - in which students from schools in different parts of the country can make recommendations on national pump design policies and on national pump maintenance policies based upon data they have collected in the survey.
The questions outlined in this investigation are meant to be suggestions: you may wish to add, or adapt this survey to suit local conditions.
If the pump is not old, or there are alternative sources of drinking water, you may wish to conduct a comparative study of pumps and other water supplies. For example, if a windlass and bucket has been recently replaced by a reciprocating pump, you may wish students to examine the pros and cons of both, basing their findings on the recent memories of water users.
Use the illustrations on page 3 of the Leaflet, and what the students have learned about pumps, to determine the pump type. Here is some additional information on reciprocating pumps to guide you:
Direct action reciprocating pumps include the Tara Pump (Bangladesh), Mark V (Malawi), Madzi (Malawi), Blair (Zimbabwe), Nsimbi (Zimbabwe), Rower (Bangladesh), Waterloo (IDREC), Wavin (Netherlands), Nira AF 85 (Finland), Ethiopia BP50 (Ethiopia), and many others.
Lever acting reciprocating pumps include the India Mark II (India), Maldev (Malawi), Afridev (Kenya), Nira AF76 (Finland), SWN 80/81 and Volanta (Holland), Petro (Sweden), Abi Vergnet (Ivory Coast), Swedpump (Sweden), Consellan and Climax (United Kingdom), National (RSA) and Bush Pump (Zimbabwe).
(from: Rural Water Supplies and Sanitation by Peter Morgan. Blair Research Laboratory, Ministry of Health, Harare, Zimbabwe published by Macmillan Publishers. London 1990)
Who's decision it was to install the pump has implications for the pump's acceptance and usage.
Who paid for and owns the pump has implications for pump accessibility.
This section is concerned with the appropriateness of the technology, (for example, are the materials locally-available and affordable? How much involvement can the community have in the construction and repair of the pump?) The students may have to ask the pump repair person to explain the materials used. The following additional information might help:
Most direct action reciprocating pumps use PVC materials below ground, and steel components above ground and are used exclusively on shallow wells down to about 12 metres in depth.
Lever acting reciprocating pumps are certainly more complex than direct action pumps and thus are generally more difficult to maintain. However, they are more robust and are essential for all deep wells and heavy duty settings, see chart below. Lever acting reciprocating pumps use steel assemblies, which support lever mechanisms. The type of lever mechanism varies considerably, but generally is based upon a steel member rotating on roller or ball bearings. More recent bearings are made of hard-wearing plastics. The Bush Pump uses a hardwood lever mechanism and a teak block as a lever and bearing surface, and this has proved very successful.
In almost all cases, pump rods are made of mild or stainless steel. The rising mains are made of galvanised or black iron or PVC. Polyethylene is used in some cases. Most cylinders are made of brass, although some are Stainless Steel. (from: Rural Water Supplies and Sanitation by Peter Morgan, Blair Research Laboratory, Ministry of Health, Harare, Zimbabwe published by Macmillan Publishers. London 1990)
Recommended settings for Handpumps
(taken from Rural Water Supplies and Sanitation by Peter Morgan, Blair Research Laboratory, Ministry of Health, Harare, Zimbabwe, published by Macmillan Publishers, London 1990)
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MAX NO. USERS
Bucket and windlass on well
NOTE: In Zimbabwe, the bucket and windlass, Bucket Pump and Bush Pump are used in programmes sponsored by the Government. The Bush Pump is used most.
This section encourages students to explore the geographical factors relating to water supply, namely the geology of the area, surface drainage, vegetation, and human settlement. Mapwork can be an integral part of the project.
Social skills may be developed through interviews. Students can create their own interview surveys and determine for themselves the effectiveness of different interviewing techniques, (e.g. open versus closed questionnaires).
The students may be able to draw some conclusions about the effectiveness of the maintenance system adopted in their community. For instance, there is evidence that where handpumps are essential for survival, in areas where water-tables are deep and there are no alternatives, communities are far more willing to contribute time and even their money to keep pumps working, since a higher value is placed on water. Where pumps are placed in areas having alternative sources of water close by, then the same principles may not apply: the users are less inclined to contribute to community maintenance, preferring to take their water from the nearest unprotected source, usually a water-hole or river, if the pump breaks down. In areas where family wells are common, these are often used in preference to communal supplies, since they are usually closer.
Encourage students to think about effective ways for the community/region to maintain its pump(s). See OUTREACH issue 76, page 15 "The barefoot mechanic".
Ask students to find out about the current procedure for getting repairs done. Is the community reliant upon outside help or is someone in the community responsible for repairs? The students may be able to suggest ways of reducing breakdowns.
Invite the students to ask others about the pros and cons of the pump. The advantages and disadvantages of pumps may not be just concerned with the design, (e.g. the pump doesn't supply water fast enough; frequent breakdowns) There could be health benefits and problems (e.g. less water-related diseases; poor hygiene as a result of sloppy pump maintenance) and social benefits and problems (e.g. the pump becomes a meeting place; time-saving way to get water, too many people trying to use pump water, the villagers are not used to - and do not like the taste or colour of groundwater). Data can be presented in bar charts and pie diagrams for analysis by students who can discover the most popular benefits and problems associated with the pump. Once identified, the students can work out ways to make improvements on the pump. Actions may vary from setting a schedule for water collection to suggestions for improving pump design.
Hand pump options for a nation
In some countries, a dozen or more different handpumps may be used, each supported by their respective donors. Discuss this issue with your students. What are the problems and potentials of having many/a few/only one pump design available in a country? Who should decide how many pump designs are available? What criteria are important for determining pump options? Consider such issues as maintenance and availability of spare parts, donor dependency, etc.)
Bucket and windlass versus reciprocating pumps
Ask your students to read this passage and then answer the questions that follow:
In Zimbabwe (1988), there are about 15,000 reciprocating handpumps in regular use, and over 50,000 bucket and windlasses. The former raises water of higher quality, but, if poorly maintained, ends up as scrap and of little use to the community it was intended to serve. The bucket and windlass is easily maintained by the community, but it often delivers water of poor quality.
1. In Zimbabwe, how many more bucket and windlasses are there than reciprocating pumps?
2. Name an advantage of a reciprocating pump over a bucket and windlass.
3. Name an advantage of a bucket and windlass over a reciprocating pump.
4. In many places of the world, the bucket and windlass remains the most successful water-lifting device ever designed. And yet this simple method has been cast aside, as being unsanitary and unsuitable for official use in most rural development programmes throughout the world. Discuss.
A pump for the village: a role playing exercise
Set up a role-playing exercise to determine which pump is to be selected for the village. Divide the class into small groups. One group is to act as a panel of local decision-makers who must decide which pump option the village should use. This group must determine the criteria on which to judge different pump designs. Here are some suggestions, taken from Water for Tanzania by PLON:
1. The operation of the pump must not require an expensive source of energy (petroleum, electricity)
2. The pump must be made of materials obtainable locally as far as possible.
3. The pump must require as little maintenance as possible.
4. The pump must be as cheap as possible.
5. The construction must be such that it will be impossible to pollute the water in or near the well.
6. The capacity of the pump must be sufficient to supply the needs of the village.
Each of the other groups studies a type of handpump in detail. The group must be familiar with the workings of the pump, the situations for which it is best suited; the materials used in its construction, and where they may be obtained; the maintenance required. Each group makes a presentation to the whole class. Then, the panel selects one pump, giving reasons for its decision.
Repairs to the Bush pump
The Zimbabwe Bush Pump is a lever acting reciprocating handpump that has been in service for over fifty years, and is still the handpump of choice in Zimbabwe (1989). There are about 15,000 Bush Pumps operating in the country.
Operating on the lift pump mechanism, the Bush Pump can lift water as high as 100 metres, but most are installed to depths of 30 and 40 metres. The pump also can be used on shallow wells.
The Bush Pump is maintained by the District Development Fund (DDF) of the Ministry of Local Government, Rural and Urban Development. The DDF operate at district level where pump fitting gangs, under the supervision of a District Field Officer, are equipped with special tools to maintain the Bush Pump and other water installations. (More recently, Pump Minders have been employed at Ward level in some areas to maintain handpumps, but this system is still being evaluated (1989).) Villagers and pump caretakers are also responsible for keeping nuts and bolts tight, greasing parts and for keeping the apron and run-off channel.
Below is a chart that shows some of the main Bush Pump repairs required in Zimbabwe (1987 -1988):
TYPE OF REPAIR
NO. OF REPAIRS
PERCENTAGE OF TOTAL REPAIRS
(from: Rural Water Supplies and Sanitation by Peter Morgan. Blair Research Laboratory, Ministry of Health. Harare, Zimbabwe published by Macmillan Publishers, London 1990)
LEAFLETS ON WATER PURIFICATION:
NO. 48: PURIFYING WATER WITH HEAT;
NO. 49: PURIFYING WATER WITH FILTERS
NO. 50: PURIFYING WATER WITH CHEMICALS
The World Health Organization (WHO) estimates that 1.2 billion people drink untreated water at considerable health risk. Eighty percent live in small rural communities, where present-day treatment units require investments far beyond their means. The Learning-By-Doing Leaflets on water purification describe some simple methods that might be applied at household or community levels.
The leaflets on water treatment are a practical way of helping students to understand various chemical processes. For example, the existence of impurities in water is a good starting point for any discussion and work on mixtures, solutions and suspensions, and experiments demonstrate how components of mixtures may be separated.
Other treatment techniques cover various other physical and chemical processes. For example, oxidisation takes place when chlorine is added to water. Physical changes (i.e. changes of state) are explored when students are experimenting with boiling water.
In the experiments using Moringa oleifera seeds, it would be best to divide the class into groups. Each group could use different quantities of Moringa seed powder, and simultaneously perform tests on water from the same source. In this way, water clarity could be compared at the same time.
Pure water boils at 100°C (212°F). The temperature does not increase after the water begins boiling. The water starts to change to water vapour before it is hot enough to boil, but the change from water to water vapour happens most rapidly at the boiling point. The amount of water being brought to a boil affects the time it takes to heat water to the boiling point. Air pressure does affect the boiling point: the higher the air pressure, the higher the boiling point.
Explain what happens to the molecules of water when it reaches the boiling point: as the molecules move faster, they move to the surface of the liquid. At the boiling point, the molecules escape from the surface of the liquid, and the liquid becomes a gas.
The sun's warmth heats the water in the bowl, making it evaporate, that is, turn into water vapour. When the vapour touches the cooler plastic sheet, it condenses back into water droplets. The water has been purified through this process, which is called distillation. The dirt and other substances that make up the mud evaporate at a much higher temperature than water does. So when the water vaporises, it leaves the particles of mud behind. This makes distillation an easy way to separate solid contaminants from water. The water collected in the glass has very few impurities and is clear. Distillation is often used when the substances in a mixture have to be separated. For instance, it's one way of making fresh water out of salt water, see GOING FURTHER.
The distilled water is absolutely pure. It can be used for drinking. It can also be used in medical prescriptions, in batteries, and in other instances where 100% chemically pure water is required.
The best results are obtained using water with few suspended particles and low bacterial density.
Ask the students to think about the size, shape and density of the sediments when determining the rates they settle out. The materials that settle first are the larger, denser materials.
Different amounts of mud come through the filters. Gravel, which permits most mud to get through, is the least effective filter. If the soil used as a filter contains clay, then the mud not only passes through but it also drags some clay with it. The sand does the best job of filtering out the solid particles. Sand cannot filter out dissolved solids such as salt and vinegar.
The effects of sand on water are complex, and involve many different mechanisms. Many bacteria are consumed by the skin on the surface of the sand. Called 'schutzdecke', this surface is made of algae, diatoms, protozoa and other organisms. When water passes between the sand grains, a process of adsorption takes place on the surface, caused by electrical and chemical bonding and mass attraction. Each cubic metre of sand provides 15,000 square metres of surface area for the adsorption of bacteria to take place. In addition, the pores or open spaces between grains occupy 40% by volume of the sand. Water flowing through these spaces slows down and sediments settle out. As the depth from the surface increases, the quantity of organic matter decreases, and the struggle between various organisms becomes fiercer. The harmful germs cannot compete with other organisms more suited to these conditions. In such an environment, disease-carrying germs perish.
Sand filters can be made in various sizes, from a family unit in a 200-litre drum or cement water jar to very large units designed for small communities.
Whilst sand removes bacteria effectively from water, it cannot easily remove large volumes of sediment which may be present in the water. Ideally, water should be added to a filter when it is mechanically clean, and this may involve pre-treatment, such as sedimentation or passing through a gravel filter first. If the water contains a lot of sediment, and this is not removed, the surface of the filter will become rapidly clogged.
OUTREACH issue 76, describes how to make a gravity sand filter for purifying water.
In the experiment, the potassium aluminium sulphate makes the small particles of clay stick together so that they filter out as if they were much larger. The particles in the liquid without the potassium aluminium sulphate get through the filter much more easily.
Using Moringa oleifera seeds
In various parts of the world, water coagulation is used to treat turbid and polluted natural waters because it does not just result in a fast removal of turbidity but also a fast removal of different types of microbes.
Studies using Moringa oleifera seeds to clarify the Nile water [Dr. Samia Al Azharia Jahn with the Deutsche Gesellschaft fhnische Zusammenarbeit (GTZ) in Germany] have found that they can "clarify Nile water of any degree of visible turbidity" At high turbidity, their action was almost as fast as alum, but at medium and low turbidities, it was slower. The doses required did not exceed 250 mg./l. Coagulating the solid matter in water so that it can easily be removed can remove a good portion of the suspended bacteria.
Powdered seeds of the Moringa oleifera tree can clarify not only highly turbid muddy water but also waters of medium and low turbidity which appear milky and opaque or sometimes yellowish or greyish. During the cool season complete clarification, which takes only one hour in hot water, may take two hours unless water is left in the sun for some time to raise its temperature.
In the case of the Blue Nile, it was found that water of low turbidity in the initial and final flood season needed doses of crushed moringa seeds equivalent to about one quarter of a seed per litre, water of medium turbidities needed half a seed per litre and at high turbidities, the dose should be 1-1.5 seeds per litre. Water from a different river will require different quantities of clarifier because of variable characteristics of suspended material. Simple experiments in jars will determine the best dose for the untreated water collected by the class.
Try to obtain seeds of the Moringa oleifera plant for students to study, to use to purify water, and to grow to obtain more seeds. If Moringa oleifera seeds are not available, try Moringa stenopetala seeds.
Oxidation occurs when other elements react chemically with oxygen. When chlorine is added to the water, it combines with the hydrogen in the water, liberating free oxygen. This oxygen rapidly oxidises matter such as bacteria which is present in the water. The amount of oxidisable matter present in the water is important, since chlorine may be used up in the oxidisation of organic matter other than bacteria. Ask the students if they think unclear water would require more or less chlorine to treat it than properly sedimented and filtered water.
ANSWERS TO QUESTIONS
In nature, the water cycle illustrates how evaporation and distillation take place. Energy from the sun causes water molecules from oceans, lakes, rivers and streams to evaporate. Up in the atmosphere, where temperatures are cooler, the water molecules slow down, get closer together and condense into tiny droplets of liquid, forming clouds. As more water molecules condense, the drops of water get bigger and bigger until they fall to earth as rain.
Sometimes, when enough water molecules are in the air and the temperature near the ground is cool enough, the water molecules condense to form dew. If the temperature drops below the freezing point (0°C or 32°F), the water in the air can change directly to ice, forming frost.
Using Moringa oleifera seeds
After stirring, the treated water should be covered and left to settle for at least an hour. If moved or shaken before this, then clarification will take much longer or fail to reach completion.
Counting the calories
The students can explore how much energy is needed to treat water with heat. For example, the class can learn about calories.
Temperature is a measure of how hot something is. To raise the temperature, you need to add heat. Nothing can get hotter unless more heat is added to it. We measure heat in calories. To raise 1ml.. of water 1°C requires 1 calorie.
(a) How many calories are needed to raise 20ml.. of water 1°C? (Answer: 20 calories)
(b) How many calories are needed to raise a litre of water from 22°C to 100°C?
(Answer: 78,000 calories)
This exercise can lead to a discussion about how much energy is needed to boil water for drinking.
The following notes on distillation are taken from Third World Science Project unit "Distillation" (produced by School of Education, University of North Wales, Bangor, UK, 1982):
(a) Solar distillation
Using a simple device as shown in the following illustration, controlled evaporation can produce fresh portable water from salt or brackish sources. A water-tight compartment, made of wood or concrete, is painted black to absorb the solar radiation which enters through the glass roof of the still. Salt or brackish water, or even sewage effluent, is allowed to flow into the channel or box to a depth of 60-100 cm. The incoming solar radiation heats the water, causing some of it to evaporate and this condenses on the inner surface of the glass roof.
GLASS COVERED SOLAR STILL
Since water will 'wet' clean glass, the condensation takes place in the form of a very thin film which flows down by gravity into the scupper which leads the condensate off to a suitable container. The water channel is insulated by the earth. After some of the water has been distilled, the brine which is left is flushed out at intervals. This prevents the concentration of salt from building up to the point when it will cover the bottom of the still with reflective white crystals.
The product of such a still is distilled water which can be used for drinking, for filling storage batteries or for any other purpose for which pure water is needed.
(b) Surviving in the desert
The diagram below is a desert survival still. The kit includes only a sheet of transparent plastic and a tin can, since the other needed materials can be found in the desert:
DESERT SURVIVAL SOLAR STILL
Even in the driest earth, there is always some moisture and it can be distilled out by creating a heat trap as shown. By using the transparent plastic cover, a rock to weigh the cover down in its centre, and a can to catch the droplets of moisture as they trickle down the inner surface of the plastic, water can be distilled. This water is suitable for drinking.
Dr. M. Kobayashi of Tokyo proved that water can be extracted from virtually any kind of soil by the still shown below:
He used a typical still construction, complete with a cover glass and reflector to increase the amount of solar radiation reaching the earth. He has tested his still at the top of Mount Fujiyama where the soil is volcanic ash and in arid deserts of Pakistan, and he has never failed to produce water which is pure and palatable.
Invite the students to construct a still for collecting water from a variety of soils in the locality. Which soil type/location/weather condition produces the most abundant water supply?
Using plants as primary coagulants
The notes above cite one water treatment study using Moringa seeds, (Dr. Jahn et al.) Another study is mentioned in CERES (134: March/April 1992) published by the Food and Agriculture Organization. Researchers from the Dept. of Environmental Technology at Leicester University (U.K.) have set up a unit at Thyolo in Southern Malawi to treat 48 cubic metres of water a day using Moringa seeds. The programme is being carried out in collaboration with local authorities, supported by the British Overseas Development Administration (ODA).
In Malawi, the pods, flowers and leaves of the tree, known locally as the Chamwamba, are the basic ingredients of the traditional local dish Ndiwo.
Moringa seeds have both economic and ecological advantages over chemicals. Malawi not only could save US$460 million a year if it no longer needed to import alum (aluminium sulphate) to purify its water, but might also be able to start cash-crop production of the seeds to stimulate the local economy. Planting the trees would help stabilise soil and contribute to the fight against deforestation.
The Moringa tree is highly resistant to drought and needs little care. It is fast-growing, produces its first seeds at 18 months and lives for an average 50 years. Each tree can produce approximately 10 000 seeds a year, and one hectare of Moringas spaced two metres apart would provide enough seeds to clarify 250 cubic metres of water every day of the year.
Working on artificially polluted water in the laboratory and then on small volumes of water taken from three rivers in Malawi, the British research team estimated the quantity of seeds needed depending upon the turbidity of the water and the volume being treated. They found that 100 milligrams of crushed seed can clear one litre of very turbid water. The study found that further disinfection (by boiling at home, or by slow filtration or chlorination at treatment sites) is still needed after treatment using Moringa seeds before the water is fit for human consumption.
The small experimental unit built at Thyolo will be the first attempt in Malawi to treat water with Moringa on an industrial scale. If the experiment is successful, similar projects will be launched in other developing countries.
For further information, write to John Sutherland, Bill Grant, Geoff Folkard or Paul William, University of Leicester, Dept. of Engineering, University Road, Leicester LEI 7RH, ENGLAND. Tel. (44) 533-522594.
Moringa oleifera seed is one of the more well known water coagulants. In certain environments, Moringa oleifera could be replaced as a "coagulant crop" by other Moringaceae (the most promising is Moringa stenopetala which has been shown to contain similar efficient primary coagulants. (Jahn 1986 and 1988). Other plant materials that are used to clarify include "Nirmali seeds" from Strychnos potatorum, sap from "tunas" (Opuntia ficus indica and other Opuntia sp.) If any of the plants are available, the students can compare their effectiveness as water coagulants. Other local available plant seeds can also be tested: the class may even discover a new coagulant!
Which water purification method is best for you?
Use this exercise to draw conclusions about water treatment techniques.
From the knowledge you have gained in the Learning-By-Doing leaflets on water purification, make up a chart similar to the one at right and complete it as best you can.
Design a water treatment plant for your community. Use some of the treatment methods described in these leaflets.
You could ask questions similar to those outlined below:
* What can be used to remove floating solids such as wood or leaves? (e.g. screening)
* How can large, non-floating solids be separated from water? (e.g. settling tanks)
* What can be used to remove suspended solids? (e.g. filtration)
* Name a way of separating dissolved chemicals. (e.g. alum)
* Which method kills all germs? (e.g. chlorine)
* Which treatment methods work well together to make water safe to drink?
(Different answers, but one might be settlement, sand filtration, and chlorine or boiling)
USING MORINGA SEEDS
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Encourage the students to apply what they have learned in these experiments to their own local conditions. They should consider which water treatment methods would suit their community bearing in mind the source of their water supply, the resources that are available and the water usage.
What do people think about water quality?
In many villages in developing countries, villagers may not seem concerned about the condition of the water they consume. Accordingly, they do not treat the water either. In such a situation it would be useless to try and disseminate water treatment technology because the people do not see the need for it.
Ask your students to find out what local people think about the quality of their water supply. Here are some possible questions. (Your students can perhaps think of others.)
* Do the people think the water they consume is dirty?
* Do they want cleaner water?
* Do they know the danger of drinking polluted water?
* Have they ever tried to treat the water they consume, and if so, how?
* Do they know of any ways to treat water?
If the survey shows few of the local people realise the danger in consuming polluted water, than invite the students to develop ways to change people's perceptions of dirty water and to make them realise its dangers. Through booklets, plays, posters and meetings etc., the students can also tell the community members about the advantages of consuming clean or treated water.
Educational Concerns for Hunger Organisation (ECHO), 17430 Durrance Road, North Fort Myers, FL. 33917, U.S.A.
ECHO'S seed bank and information network help Third World farmers to farm better with the skill, tools, and condition they have to work with. If you are planning to start a nursery for Moringa seeds, write to ECHO requesting information. In particular, ECHO Technical Note A-5 describes the uses and cultivation of Moringa oleifera. Explain in your letter the reason for your inquiry and ECHO may be able to provide some seeds, too.
A publication that may be of interest is Traditional Water Purification in Tropical Developing Countries by Samia Al Azharia Jahn, 117 GTZ (Deutsche Gesellschaft fhnische Zusammenarbeit) Eschborn, Germany, 1981. This manual deals with a scientific appraisal of indigenous technologies in the tropics for the improvement of water quality.
GATE No. 1/1989 includes information on water purification using Moringa oleifera seeds. GATE is produced by Deutsche Zentrum fwicklungstechnologien, Dag-Hammarskjold-Weg 1, D-6236 Eschborn 1, Germany.
WATERLINES, Vol. 3, No. 4, April 1985 (published by IT Publications, 103-105 Southampton Row, London WC1B 4HH UK) also has an article on water purification using Moringa oleifera seeds. The article describes how Dian Desa, an Indonesian NGO, has used Moringa oleifera seeds in water purification projects in rural areas. Villagers' perceptions about water treatment are discussed, as are the ways Dian Desa changed these perceptions and encouraged the use of Moringa oleifera (known as kelor in Indonesia). A method of treating the water is also described:
Two clay jars are used. The settling occurs in one and the clarified water is stored in the second. Jars are modified slightly by the addition of an outlet to siphon the treated water. This is because the protein in dissolved kelor seeds will start to ferment and small after about 12 hours.
(1) Turbid water poured into the first pot for treatment.
(2) Bung removed from outlet of first pot. Clarified water stored in the second. The lower outlet is used to drain the jar.
For more information, contact Dian Desa, Jalan Kaliurang KM 7, P.O. Box 19, Bulaksumur, Yogyakarta, Indonesia.