The primary purpose of the Guidelines for drinking-water quality is the protection of public health. The Guidelines provide the recommendations of the World Health Organization (WHO) for managing the risk from
hazards that may compromise the safety of drinking-water. The recommendations should be considered in the context of managing the risk from other sources of exposure to these hazards, such as waste, air, food and consumer products.
The Guidelines are regarded globally as the most authoritative framework on drinking-water quality and often form the basis for national laws and regulations.
The Guidelines provide an evidence-based point of departure for standard setting and regulation as a basis for health protection. They include an assessment of the health risks presented by the various microbial, chemical, radiological and physical constituents that may be present in drinking-water. While the guidance is advisory in nature, health-based guideline values for hazardous constituents are derived and presented as maximum recommended concentrations.
The Guidelines promote a framework for safe drinking-water, composed of health-based targets, water safety plans, and independent surveillance.
In the 4th edition, substantial new text has been introduced on how to implement these Guidelines, including on adapting these to national/local circumstances, for example through the establishment of interim standards to encourage step-wise improvements in resource-limited contexts.
It has new guidance on emerging issues of public concern like pharmaceuticals in drinking-water and the chapter on radiological aspects has been comprehensively revised. New or improved explanations have been incorporated on how to more effectively manage drinking-water quality in a range of specific circumstances including: climate change risks, emergencies, bulk water supplies, household-level water management including rainwater harvesting and point-of-use treatment and safe storage.
New or revised risk assessments have been applied to over thirty chemical and microbial hazards, including emerging organisms of concern. New guidance has been formulated on applying pesticides to drinking-water for public health purposes (e.g. to control mosquito larvae in potable water containers in order to prevent dengue transmission).
There are also revised guidelines for key chemicals responsible for large-scale health effects through drinking-water exposure, including arsenic, fluoride and lead, and chemicals of public concern such as nitrate, selenium, uranium and disinfection-by-products.