Drinking water quality

Safe drinking water is a basic need for human development, health and well-being. Theoretically, it is possible to assess at a national or local level the health risks from chemicals in drinking water for every chemical for which a guideline has been set. The World Health Organization (WHO) has published procedures for assessing chemical health risks. These assessments may be used to manage chemical risks to water safety by the development of control and monitoring programs and of national standards for drinking water quality.

However, to make such assessments and develop management strategies for every chemical would be impractical. A more effective approach where resources are limited is to identify and focus on those priority chemicals for which significant human exposure is expected to occur, recognizing that priorities may vary from country to country, and within countries.

In many countries, the development of appropriate risk management strategies is hampered by a lack of information on the presence and concentration of chemicals in drinking water. Water authorities attempting to identify priority chemicals despite having limited information would benefit from guidance on simple and rapid assessment methods. These could be applied at a national or local level to provide a shortlist of priority chemicals, which could then be more rigorously assessed for health risks (WHO 1994; 1999).

The WHO Guidelines for Drinking-water Quality cover both microbial and chemical contaminants of drinking water and describe in detail the scientific approaches used in deriving guideline values for those contaminants. They thus provide sound guidance for ensuring an appropriate level of safety and acceptability of drinking water for the development of national standards, while taking into consideration the specific problems and cultural, social, economic and environmental conditions of a particular country.

The criteria for including specific chemicals in the WHO Guidelines for drinking water quality are any of the following:

-    there is credible evidence of occurrence of the chemical in drinking water, combined with evidence of actual or potential toxicity

-     the chemical is of significant international concern

-     the chemical is being considered for inclusion, or is included, in the WHO Pesticide Evaluation Scheme (WHOPES) program

Applying these criteria, the guidelines list nearly 200 chemicals for which guideline values have been set or considered. This number may change over time. It is important to note that the lists of chemicals for which WHO guideline values have been set do not imply that all those chemicals will always be present, nor do they imply that specific chemicals for which no guideline values currently exist will not be present in a water supply. However, it is not necessary for national or local authorities to develop risk management strategies for each and every chemical for which guideline values have been set, but rather to identify and select those chemicals that may be of greatest priority for risk management purposes in the particular setting (WHO, 2004; 2006).

Drinking-water standards and guidelines

Every country should have a policy on drinking-water quality. The nature and form of drinking-water standards may vary between countries and regions – no single approach is universally applicable. Approaches that may have worked in one country or region do not necessarily transfer to other countries. It is essential that each country undertake a review of its needs and capacity for drinking-water standards before embarking on the development of a regulatory framework.

National and regional standards should be developed from the scientific basis provided by the WHO Guidelines for Drinking-water Quality, adapted to take account of local or national environmental, sociocultural and economic conditions. The guidelines provide further information on the development and implementation of national standards.

The implementation of a successful risk management strategy requires the development of an understanding of those hazards that may impact on the quality of water being provided to a community. A wide range of chemicals in drinking-water could potentially cause adverse human health effects. The detection of these chemicals in both raw water and in water delivered to consumers is often slow, complex and costly, which means that detection is too impractical and expensive. Thus, reliance on water-quality determination alone is insufficient to protect public health.

As it is neither physically nor economically feasible to test for all drinking-water quality parameters, monitoring effort and resources should be carefully planned and directed at significant or key characteristics. A preventive management strategy, operating from the water catchment to the tap, should be implemented to ensure drinking-water quality. The strategy should combine protection of water sources, control of treatment processes and management of the distribution and handling of water.

The management procedures developed by water suppliers can be described as a water safety plan. The water safety plan should address all aspects of the water supply and should focus on the control of water production, treatment and delivery of drinking-water, up to the point of consumption. The plan provides the basis for a process control methodology to ensure that concentrations of chemicals are acceptable (Thompson et al., 2007).


  • Thompson T., J. Fawell, S. Kunikane, D. Jackson, S. Appleyard, P. Callan, J. Bartram and P. Kingston (2007). Chemical safety of drinking-water: Assessing priorities for risk management, World Health Organization, ISBN 978 92 4 154676 8.
  • WHO (1994). Environmental Health Criteria Document No. 170 Assessing human health risks of chemicals: derivation of guidance values for health-based exposure limits, World Health Organization, Geneva.
  • WHO (1999). Environmental Health Criteria Document No. 210. Principles for the assessment of risks to human health from exposure to chemicals, World Health Organization, Geneva.
  • WHO (2004). Guidelines for Drinking-water Quality, 3rd ed., Volume 1: Recommendations, World Health Organization, Geneva.
  • WHO (2006). Guidelines for Drinking-water Quality, 1st Addendum to the 3rd ed., Volume 1: Recommendations, World Health Organization, Geneva.



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