Some simple ways to purify drinking water

Drinking water is not always safe. Sometimes it can carry debilitating diseases, even death. To prevent infection by waterborne diseases, follow the simple techniques given below.

Boiling

Boil all drinking water for at least 10 minutes. Boiling kills most of the harmful organisms present in water. In case boiling is a problem-because of high fuel costs or lack of fuel-boil at least the water for children, older people, and sick people, especially during the rainy season. To improve the taste of boiled water, stir it vigorously with a clean spoon or pour the water from a height, from one container to another several times.

Copper or brass vessels

If possible, store water in copper or brass vessels.

Copper and brass inhibit the growth of bacteria.

Solar disinfection

1 Leave water containers for some time so that heavy dust and dirt particles settle to the bottom.

2 Pour the water into transparent plastic, coloured glass, or blue-tinted glass vessels or bottles. As you pour, be very careful not to disturb the sediment.

3 Cover the vessels and cap the bottles.

4 Expose them to strong direct sunlight for at least 90 minutes. If possible, put the vessels in the sun early in the morning and leave them out until late afternoon. This destroys bacteria that cause several common diseases. Keep the vessels slightly away from each other for direct radiation.

Transparent plastic and colored glass vessels

This solar-disinfected water can be used directly or kept overnight to cool.

Three-pot system

Unsafe, dirty water can be made much safer simply by storing it for at least 24 hours Within that time most of the dirt will sink to the bottom.

1 Take two big pots and one small pot. Use the big pots for fetching water on alternate days.

2 Allow the water in the first pot to stand for 24 hours.

3 Then, pour the clear top water into the small Pot for drinking.

4 Use the remaining water for washing.

5 Clean and refill the first pot when it is empty.

6 Again, allow it to stand for 24 hours.

7 Use the second pot in the same way as the first. In this way, each day's drinking water has been left to stand for at least 24 hours.

Double-layered cloth

Cloth filters

Cloth water filters can be used to strain insects, worm larvae and other comparatively large particles from water. Make a simple two-layer filter using cloth of two different colours so that you know which side to place on top (to receive unclean water). Use tightly woven cloth. Wash the filters after each use. This prevents organisms and debris caught in the filter from recontaminating the water. You can also buy readymade, cheap plastic filters.

Cloth filters

Charcoal filters

Charcoal water filters can be used to remove suspended material and harmful bacteria in polluted water to a level satisfactory for human consumption.

Water-filter pot

Materials

- Gravel and sand for filtration.
- Charcoal to remove colour, odour, taste, and certain dissolved impurities

Construction

1 Make a number of small holes in the bottom of a galvanized iron or steel drum, clay pitcher, or ordinary steel drum. This will be the water-filter container.

2 Fill the pitcher or drum with a 25-cm layer of gravel.

3 Place a layer of coarse sand on top of the gravel, up to a height of about 25 cm.

4 Cover with charcoal.

5 Cover the charcoal with a 510-cm thick layer of gravel to prevent the charcoal pieces from floating in the water.

Chemical disinfection

Chlorine in one form or another is the most common chemical used for disinfection of water It is normally effective against bacteria commonly associated with water-borne diseases It is, however, less effective against certain cysts, ova, and viruses

Chlorine is supplied as a gas, in solution, or as a solid. Probably the easiest form of sterilization of emergency water supplies is by use of either calcium hypochlorite (ordinary bleaching powder) or sodium hypochlorite (available as a liquid).

Notes

- Wash the materials before filling the filter container.

- About three-quarters of the drum should be filled with the filter material. Place this water-filter container on top of another iron or steel drum or clay pitcher, fitted with a tap. Pour water in the top. Filtered water is obtained through the tap at the bottom. The charcoal should be replaced after six months. The sand and gravel can be washed and reused.

- You are advised to add a few drops of chlorine solution (5.25 percent) to disinfect each jug of water.

Chlorination at home

Make a chlorine solution by mixing 1 cup of laundry bleach in 3 cups of water. Add 3 drops of this solution to 1 litre of water and allow the water to sit for 30 minutes. Alternatively, you can treat water using chlorine tablets which are available in the market.

Chlorination of community wells
Continuous disinfection of well water can be done using low-cost devices called "pot chlorination "

Single-pot chlorinator-for larger wells

1 Take a 12- 15 litre earthen pot.

2 Make two holes 0.6 cm in diameter in the middle of the pot.

3 Pour into the pot a moist mixture of 1.5 kg bleaching powder and 3 kg coarse sand. (The mixture should occupy the volume of the pot below the level of the holes).

4 Cover the mouth of the pot with polythene.

5 Lower the pot into the well with a rope so that it remains 60 cm below the surface of the water.

Single-pot chlorinator

This unit can chlorinate wells holding 9,000-13,000 litres of water with a withdrawal rate of 900-1,300 litres per day (sufficient for 40-60 people per day) for a period of at least one week. The treated water has a chlorine content of 0.2-0.8 parts per million.

Double-pot chlorinator-for small household wells

Use of a single-pot chlorinator in a small well (4,000 litres of water with a withdrawal rate of 360-450 litres per day) will result in over-chlorination. Instead, use a double-pot chlorinator.

1 Take two cylindrical pots-one to fit inside the other.

Double-pot chlorinator (cutaway view)

2 Make a 1 cm diameter hole in the side of the smaller pot, about 8 cm below the rim.

3 Fill this pot to just below the hole with a moist mixture of 1 kg bleaching powder and 2 kg coarse sand.

4 Make a hole 1 cm in diameter, about 4 cm from the bottom of the big pot.

5 Put the small pot inside the big pot.

6 Cover the mouth of both pots with polythene.

7 Lower the unit into the well with a rope so that it hangs 1 m below the water level. This chlorinator gives 0.3-0.5 parts per million of chlorine over a period of 2-3 weeks.

Sources: National Drinking Water Mission, Government of India, Mr. Yas Pal Bedi, and Directorate of Advertising and Visual Publicity, Government of India

Calculating volume

Use this formula to calculate the volume of water in your well:

3 x radius of the well (cm) x radius of the well (cm) x depth of water (cm) = cubic cm