Water supply standard 2: Water quality
Water is palatable and of sufficient quality to be drunk and used for cooking and personal and domestic hygiene without causing risk to health.
Key actions (to be read in conjunction with the guidance notes)
Undertake a rapid sanitary survey and, where time and situation allow, implement a water safety plan for the source (see guidance notes 1–2).
Implement all necessary steps to minimise post-delivery water contamination (see guidance notes 3–4 and Hygiene promotion standard 1 on page).
For piped water supplies, or all water supplies at times of risk of diarrhoeal epidemics, undertake water treatment with disinfectant so that there is a chlorine residual of 0.5mg/l and turbidity is below 5 NTU (nephelolometric turbidity units) at the tap. In the case of specific diarrhoeal epidemics, ensure that there is residual chlorine of above 1mg/l (see guidance notes 5–8).
Where household-level water treatment is proposed, ensure that it is accompanied by appropriate promotion, training and monitoring (see guidance notes 3 and 6).
Key indicators (to be read in conjunction with the guidance notes)
There are no faecal coliforms per 100ml of water at the point of delivery (see guidance note 2).
Any household-level water treatment options used are effective in improving microbiological water quality and are accompanied by appropriate training, promotion and monitoring (see guidance notes 3–6).
There is no negative effect on health due to short-term use of water contaminated by chemicals (including carry-over of treatment chemicals) or radiological sources, and assessment shows no significant probability of such an effect (see guidance note 7).
All affected people drink water from a protected or treated source in preference to other readily available water sources (see guidance notes 3 and 6).
- There is no outbreak of water-borne or water-related diseases (see guidance notes1–9).
1. A sanitary survey and water safety plan: A sanitary survey is an assessment of conditions and practices that may constitute a public health risk. It covers possible sources of contamination to water at the source in transport and in the home, defecation practices, drainage, and solid waste management. Community mapping is a particularly effective way of identifying where the public health risks are and thereby involving the community in finding ways to reduce these risks. Note that while animal excreta is not as harmful as human excreta, it can contain micro-organisms, such as cryptosporidium, giardia, salmonella, campylobacter, caliciviruses and other common causes of human diarrhoea, and therefore presents a significant health risk. WHO recommends the use of its water safety plan (WSP), which is a holistic approach covering hazard identification and risk assessment, an improvement/upgrade plan, monitoring of control measures, and management procedures, including the development of supporting programmes (see References and further reading).
2. Microbiological water quality: Faecal coliform bacteria (>99 per cent of which are E. coli) are an indicator of the level of human and/or animal waste contamination in water and the possibility of the presence of harmful pathogens. If any faecal coliforms are present, the water should be treated.
3. Promotion of protected sources: Merely providing protected sources or treated water will have little impact unless people understand the health benefits of this water and therefore use it. People may prefer to use unprotected sources, e.g. rivers, lakes and unprotected wells, for reasons such as taste, proximity and social convenience. In such cases, technicians, hygiene promoters and community mobilisers need to understand the rationale for the preferences so that their consideration can be included in promotional messages and discussions.
4. Post-delivery contamination: Water that is safe at the point of delivery can nevertheless present a significant health risk due to recontamination during collection, storage and drawing. Steps that can be taken to minimise such risk include improved collection and storage practices and distribution of clean and appropriate collection and storage containers (see Water supply standard 3). Water should be routinely sampled at the point of use to monitor the extent of any post-delivery contamination.
5. Water disinfection: Water should be treated with a residual disinfectant such as chlorine if there is a significant risk of source or post-delivery contamination. This risk will be determined by conditions in the settlement, such as population density, excreta disposal arrangements, hygiene practices and the prevalence of diarrhoeal disease. In the case of a threat or the existence of a diarrhoea epidemic, all drinking water supplies should be treated, either before distribution or in the home. For water to be disinfected properly, turbidity must be below 5 NTU, although for short-term emergency use, water of higher turbidity can be adequately disinfected with double chlorine dosage after filtration until turbidity reduction is achieved (see Appendix 6: Household water treatment and storage decision tree).
6. Household-level water treatment: When use of a centrally operated water treatment system is not possible, point-of-use water treatment (PoUWT) at household level can be used as an option. The different types of PoUWT options shown to reduce diarrhoea and improve the microbiological quality of stored household water include boiling, chlorination, solar disinfection, ceramic filtration, slow sand filtration and flocculation/disinfection. The most appropriate PoUWT option for any given context depends on existing water and sanitation conditions, water quality, cultural acceptability and the implementation feasibility of any of the options. Successful PoUWT should include the provision of adequate materials and products and appropriate training for the beneficiaries. Introducing an untested water treatment option in a disaster should be avoided. In areas with anticipated risk, pre-placement of PoUWT products should be considered to facilitate a quick response. The use of locally available products should be prioritised if continued use in the post-disaster phase is desired. Effective use of PoUWT requires regular follow-up, support and monitoring and this should be a prerequisite to adopting it as an alternative water treatment approach.
7. PoUWT using chlorine: Double-dose chlorination can be considered for higher turbidity where there is no alternative water source. This should be attempted only for short periods of time and after educating users to reduce turbidity by filtering, settling and decanting before treatment (see Appendix 6: Household water treatment and storage decision tree).
8. Chemical and radiological contamination: Where hydrogeological records or knowledge of industrial or military activity suggest that water supplies may carry chemical or radiological health risks, the risks should be rapidly assessed by carrying out a chemical analysis. A decision that balances short-term public health risks and benefits should then be made. Furthermore, a decision to use possibly contaminated water for longer-term supplies should be made on the basis of a more thorough assessment and analysis of the health implications.
9. Palatability: Taste is not in itself a direct health problem (e.g. slightly saline water does not pose a health risk), but if the safe water supply does not taste good, users may drink from unsafe sources and put their health at risk. To avoid this, hygiene promotion activities are needed to ensure that only safe supplies are used.
10. Water quality for health centres: All water for hospitals, health centres and feeding centres should be treated with chlorine or another residual disinfectant. In situations where water is likely to be rationed by an interruption of supply, sufficient water storage should be available at the centre to ensure an uninterrupted supply at normal usage levels (see Appendices 2: Minimum water quantities for institutions and other uses and 5: Minimum hygiene, sanitation and isolation activities for cholera treatment centres).