The guidance provided in this document focuses on applying the framework for safe drinking-water, including Water Safety Plans (WSPs), as described in the fourth edition of the "Guidelines for Drinking-Water Quality" (WHO, 2011). The scope of this document includes small to large piped water systems in both developed and developing countries. It applies from the outlet of primary treatment processes to delivery to consumers, including at standpipes, but does not include pipework within buildings either before or after the point of delivery. This is the subject of the complementary text on Water Safety in Buildings. The main text is divided into 12 sections following the descriptions in the "Guidelines for Drinking-Water" Quality (WHO, 2011) and based on the 11 modules included in the "Water Safety Plan Manual" (2009), with an additional section describing the enabling environment (policy and regulations, independent surveillance and disease surveillance). It is important for regulatory and policy frameworks to support the implementation of WSPs to ensure their successful application. A number of case-studies are provided as annexes to illustrate the challenges that can confront drinking-water suppliers and potential solutions to overcome these challenges.