This new edition of WHO's Guidelines for Drinking-water Quality provides a state-of-the art perspective on issues of water quality and health and on effective approaches to water safety management. The Guidelines are used by countries worldwide as a scientific basis for standard setting and regulation and are used extensively by professionals and local decision-makers. They supersede five editions of guidelines and of previous International Standards. This fully revised third edition includes expanded coverage on systematic drinking-water safety assessment and management. It describes a Water Safety Framework, encompassing complementary functions of national regulators, water suppliers and independent surveillance agencies. The Water Safety Plan provides a comprehensive approach to assist suppliers in water safety management. Guideline Values for individual chemicals have been reviewed, updated and newly added in response to available scientific information. Summary statements are included for specific pathogens and individual chemical hazards of actual or potential concern. This third edition also includes more information on application of the Guidelines in specific circumstances (e.g. small community supplies, in large buildings, in emergencies and disasters); and to specific applications (e.g. bottled water). Volume 1 of the Guidelines also provides a roadmap to more than 130 documents, which substantiate or explain the content of the Guidelines, and to a large series of guidance documents on good practice in achieving drinking-water safety. See also Addendum to volume 1