Water Engineering and Development Centre
Author(s): Skinner, BrianPublisher: LSHTM | WEDC
Series: WELL Studies in Water, Sanitation and Environmental Health Task 511
This study is about the use of chlorination to disinfect water in small water supply systems in low and middle-income countries. Emphasis is on gravity or water-powered systems ideal where electricity is unavailable. Chlorine gas is not considered in the report because it is not widely available in low to middle-income countries. Further the risks of using chlorine gas (which is very poisonous) in such environments is considered unacceptable.
The introduction sets chlorination in its right context. It discusses the quality of water sources and suggests that efforts should be made to use water that does not need disinfecting. It discusses the role of hygiene education in encouraging consumers to protect chlorinated water between collection and consumption. The supposed risks associated with by-products of chlorine (eg cancer) and also the resistance of pathogens to chlorine is examined. Other issues examined include taste and odour, and the small-scale production of sodium hypochlorite.
The second section of the report introduces chlorination and the variables that affect its working. These include contact time, chlorine concentration, type of chlorinator, water flow rate and water characteristics. The following section describes gravity-driven, water-powered and diffusion chlorinators. A guide for selecting chlorinators for small water supplies follows this. The main criteria for selecting chlorinators include the nature of the flow of water to be treated; the origin of the doser and its operation /maintenance requirements; the type of chlorine compound available; and the ability of the doser to cope with changes in water level or pressure. Two tables are provided to guide selection for different water sources, flow regimes and local constraints.
Information about suppliers of chlorinating kits, test equipment and small electrolysis units used to produce sodium hypochlorite is found in Appendix 1. In Appendix 2, is devoted to the recent development of simple electrolysis units that can be used to produce sodium hypochlorite from brine, which is itself made from water and common salt.
The booklet concludes with the message that the most practical way to disinfect small water supplies remains chlorination. There exists a wide variety of non-electrically powered chlorniators, many of which can be constructed using basic materials. The technology is now available to allow the production of sodium hypochlorite at even the village level in poorer countries. Thus one impediment to chlorination has been overcome.