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close this bookOutreach N 86 - Learning by Doing - Leaflets on Pressure and Water Technologies (OUTREACH - UNEP - WWF, 64 p.)
close this folderSection II: Water Technologies
View the documentLeaflet no. 39: Your community's water supply
View the documentLeaflet no. 40: Catch a falling raindrop
View the documentLeaflet no. 41: Building small dams
View the documentLeaflet no. 42: Sinking wells
View the documentLeaflet no. 43: Water-lifting devices (1) Using simple machines
View the documentLeaflet no. 44: Water-lifting devices (2) Siphons
View the documentLeaflet no. 45: Water-lifting devices (3) Suction pumps
View the documentLeaflet no. 46: Water-lifting devices (4) Force pumps
View the documentLeaflet no. 47: Pump probe and patrol
View the documentLeaflet no. 48: Purifying water with heat
View the documentLeaflet no. 49: Purifying water with filters
View the documentLeaflet no. 50: Purifying water with chemicals

Leaflet no. 50: Purifying water with chemicals

Does your water contain harmful germs? It can be purified by adding various chemicals to it. After learning about all these techniques, try them for yourself, compare the results, and decide which works best for you.


Filters can remove small particles that are suspended in water, but some particles are too small to be filtered out. If a chemical called potassium aluminium sulphate is added to water, it makes tiny particles group themselves together or coagulate. When the water is then filtered, these grouped particles are large enough to be removed from the water. You can observe coagulation by trying the following experiment. You will need:

* powdered potassium aluminium sulphate (Al2(SO4)3.K2SO4)
* a small amount of clay;
* some sand;
* 2 funnels;
* filter paper,
* 2 upright stands and 2 ring supports;
* 4 pint jars.


Arrange the stands, ring supports and funnels lined with filter paper as shown in the diagram at right.

Put about 1 inch of sand in each of the runnels. Mix 2/3 of a cupful of water and 2 teaspoonfuls of clay in one jar. Make a similar mixture in another jar, but also add 2 teaspoonfuls of potassium aluminium sulphate. Stir both mixtures. Pour each mixture through a different runnel into clean pint jars. Compare the liquids you catch in the pint jars. Which one holds the cleanest water?

Advantages: Coagulation is a process that can be used to filter out very tiny particles of clay. It can also remove remains of germs that have been killed by other means but which are too small to be filtered out by means of sand and gravel alone.

Disadvantages: This process cannot remove dissolved industrial wastes. It cannot purify liquid sewage or germ-polluted water either. The liquid sewage contains dissolved impurities, and germs are usually too small to be filtered out in this particular way. Coagulation must be done in association with filtration or settlement. Use of chemical coagulants may require trained personnel.


Native to Northern India, the multipurpose Moringa oleifera trees is widespread in semi-arid subtropical countries, and are known by many different names, for example, malunggay (the Philippines) and benzolive tree (Haiti). The fast-growing tree, is a source of fruit, leafy vegetable, fodder, herbal medicine, nectar for bees, natural fences, fuel and raw materials for paper mills. The idea of using Moringa tree seeds to clear water came from Sudan, where -women use the seeds to clarify muddy water from the Nile River in large earthenware jars. The crushed seeds coagulate particles suspended in the water including types of disease organisms. Agglomerates which form fall to the bottom of the jars where they can be collected.


How to purify water using Moringa oleifera seeds.

You need:

* 1 litre of turbid water (not drawn after sudden heavy rains or sandstorms as these will increase the amount of coagulant needed);

* some clean (clarified) water,

* a small bottle or cup;

* a mortar and pestle

* a clean cotton cloth or fine mesh tea strainer,

* a ladle;

* a container (with well-fitting lid) that can hold a litre of water.

* a Moringa oleifera seed;

* a stirring spoon;

* a small cup;

* spoon;

* 2 glass jars for samples;

1. Remove wings and brown coat of the seed; discard any seed kernels (cotyledons) that have dark spots or other signs of damage.

2. In a mortar, crush the seed into a fine powder.

3. Put the powder into a small bottle, and add clean water by a measured spoon (or use a home-made graduated bottle) to make a 2% suspension.

4. Stir or shake vigorously for 5 minutes to obtain a watery extract of the coagulant.

5. Filter the suspension through a clean cotton cloth into a small cup.

6. Put a litre of turbid (muddy) water into a container. Stir the water fast, and after a few seconds, while still stirring, add the milky suspension. Continue stirring for 30 - 60 seconds.

7. Continue stirring slowly and steadily (about 20 rotations per minute) for 5 minutes. You can control the stirring movement by chanting phrases to maintain a rhythm.

8. Cover the container with a lid, and allow the floc (solid matter) to settle. Leave undisturbed, and then take water samples using a ladle after (a) 1 hour (b) 2 hours.

9. Put the samples into glass jars. Assess the result with the naked eye. Record your observations in a chart similar to the one below.


Extension: Experiment further by varying the following:

(i) the quantity of moringa seed powder used (for example, use (a) ¼ seed (b) ½ seed (c) 2 seeds (d) 3 seeds per litre of raw water);

(ii) the time and intensity of the stirring of the raw water and the milky solution.

What happens if, after stirring, the treated water is disturbed and not allowed to settle for at least an hour?

Compare the required treatment of waters of different turbidity. For example, treat water taken from a river before and just after a sudden rainstorm.

Advantages: It is a simple, cheap way to obtain clear water. It improves the physical, chemical and microbiological quality of the water. The method uses equipment found locally. No side effects to health have been associated with the use of Moringa oleifera seeds. Using locally-grown seeds means a country no longer needs to import alum (aluminium sulphate) to purify water.

Disadvantages: Often unaware of how much the amount of suspended matter in raw water fluctuates, people may use random dosage and unsuitable application methods. If "clarified" water appears whitish, not clear, its quality may be little better than if it had simply been left to settle for 24 hours. Although a significant percentage of indigenous bacteria are removed through treatment, scientific studies suggest treated water should be further purified by filtration, chorination or boiling. To achieve uniform results, equipment needs to be standardised; appropriate training given; daily water treatment activities monitored. The treated water must be left undisturbed for at least one hour for purification to be effective. Favourable growing conditions are needed to produce the seeds, although the tree does seem to thrive in impossible places: near the sea, in bad soil and dry areas. Cultivation requirements vary according to environmental conditions.

Try this: If growing conditions are appropriate, set up a nursery for the seeds.


Another way to disinfect water is to buy special chemicals, which when added to water, will kill all harmful organisms. Often people add chemicals after it has been filtered to make sure it is completely safe. The most common chemical for disinfecting water is chlorine. You may have come across chlorine because it is found in bleaching powder.

Chlorine kills germs chemically, but you would have to go to a biology laboratory to perform experiments proving this. You would grow cultures (colonies grown in a test tube) of harmful bacteria and then kill them with chlorine. Both these things would be too dangerous to try at home. Furthermore, chlorine, in sufficient amounts, is a poisonous gas and is very dangerous to work with.

For disinfecting a large water supply, chlorine is put into the water as a gas. For small communities, it is best to use chlorine tablets. When added to water, the tablets dissolve and the chlorine kills the germs. It always takes time for the chlorine to work. If you try this, allow at least 30 minutes for the chlorine to take effect.

In whatever form the chlorine is used, the dosage of available chlorine must be carefully measured. For example, the eggs of worms and organisms that cause bilharzia need very strong doses of chlorine solution to kill them. However, these organisms can be filtered out before a chlorine solution is added so that less chlorine is needed to kill other disease organisms.

Advantages: Chemicals, when added to water, kill all harmful germs.

Disadvantages: Chemicals are expensive and probably must be imported. They are difficult to handle, and sometimes require a trained operator.

OUTREACH pack 86 pp 29-30. Other Learning-By-Doing Leaflets and Information packs are available from Dr. James Connor, OUTREACH Director, Environmental Education Center, 200 East Building, New York University, New York NY 10003, U.S.A. or Richard Lumbe, OUTREACH Coordinator, Information & Public Affairs, UNEP, P.O. Box 30552, Nairobi, KENYA