FRESH Tools for Effective School HealthFirst Edition
Water quality is determined on the basis of an indicator of faecal contamination, namely the concentration of Escherichia coli (E. coli)iii. The level of free residual chlorine at the point of water delivery is another indicator. Free residual chlorine should be kept at 0.20.5 mg/litre to reduce the risk of microbial regrowth. The detection of chlorine in this concentration range provides an indication of the absence of contamination.
1.3Minimal Acceptable Standards
While bearing in mind that action should be taken to ensure that the above optimal standards are met, the following are the minimal acceptable standards.
Everyone requires about two litres of water a day for basic physiological needs.
As a minimum, school students would manage, under difficult conditions and for a limited period of time, with an amount of at least 5 litres of water per day per student for drinking and cooking.
Water can be freed of pathogens (disease-causing microorganisms) by bringing it to a vigorous boil for 1 minute. Boiling, however, has the following main disadvantages:
fuel is required (about 1 kilogram of wood is needed to boil one litre of water);
water can be contaminated again when it has cooled.
Chlorine is a very effective disinfectant. Water can be chlorinated at the school level (see Simple Technology for Filtering and Disinfecting Water at School). About 4 grams of active chlorine are required for disinfecting one cubic meter (1000 litres) of water. As active chlorine costs approximately US $ 7 per kilogram, the cost of disinfecting 1000 litres of water, which would cover the minimal acceptable drinking and cooking needs of about 200 students per day, would be about 3 US cents.
Turbidity (cloudiness) can be caused by silt, sand or mud as well as by some microorganisms. Turbid water should be filtered before it is chlorinated. There are various types of filters that not only reduce turbidity but also inactivate most pathogens present in the water. Where "commercial candle filters" are not available in the market, household filters can be prepared, as shown in the above-mentioned tool.
Water from unreliable sources should always be disinfected.
Chlorination is preferable to other traditional methods as it is reliable and less expensive. If chlorine compounds are lacking, the water should be boiled.