Safe and clean drinking-water is an essential element of health security and underpins sustainable socio-economic development. Global climate change, a growing global population, water requirements to support food security and rapid urbanization all contribute to increased water scarcity and compound the challenge of providing safe drinking-water. In many parts of the world there is a need to develop and manage alternative sources of safe drinking-water. This WHO guidance document is health-focused and it builds on the publication “Desalination technology: health and environmental impacts” which covers the broader context of environmental, technical and operational aspects of desalination.