In 2003, UN-Water was endorsed as the new official United Nations mechanism for follow-up of the water-related decisions reached at the 2002 World Summit on Sustainable Development and the Millennium Development Goals. It will support Member States in their efforts to achieve water and sanitation goals and targets.

UN Water's work encompasses all aspects of freshwater, including surface and groundwater resources and the interface between fresh and sea water. It includes freshwater resources, both in terms of their quality and quantity, their development, assessment, management, monitoring and use (including, for example, domestic uses, agriculture and ecosystems requirements).

The scope of the work of UN-Water also includes sanitation - encompassing both access to and use of sanitation by populations and the interactions between sanitation and freshwater. It further includes water-related disasters, emergencies and other extreme events and their impact on human security. UN-Water acts at global, regional and country level. It adds value to the work and expertise of separate UN agencies and programmes. It brings coherence and integration among them, and serves as the common voice of the UN system on water and sanitation. It will improve cooperation with external partners, and provide timely information on status and trends of the world's freshwater resources.

UN-Water is responsible for organizing the annual United Nations World Water Day (22 March) and the up-coming United Nations Decade on Water 2005 - 2015.

UN Water is made up of the UN agencies, programmes and funds that have a significant role in tackling global water concerns. It also includes major non-UN partners who cooperate with them in advancing progress towards the water-related goals of the Decade Water for Life and Millennium Declaration.

UN-Water is responsible for assessing status and trends in freshwater at the global and regional levels. It achieves this through two major periodic publications. The World Water Development Report is a periodic, comprehensive review providing an authoritative picture of the state of the world's freshwater resources. The Joint Monitoring Programme for Water Supply and Sanitation reports on the status of water supply and sanitation.

Other global monitoring initiatives relevant to the water sector include

The Human Development Report
The World Bank Economic Development Report
The Habitat Cities report
The UNEP Global Environmental Outlook
The state of food insecurity in the world
The state of the world’s children

Coherence of UN-system actions at the country level is crucial to achieving the overall objectives underlying the establishment of UN-Water. Many of the UN organisations that form UN-Water have operational activities at country level, and UN-Water is not a mechanism for direct implementation. UN-Water’s contribution to country-level coherence consists largely of “communication” actions in support of progress towards relevant MDG targets. To this end, the UN system provides access to a range of country-level policies and assessments, including:

National poverty reduction strategies
National assessment reports for the World Summit on Sustainable Development
National Implementation of Agenda 21 - 2002 Country Profiles
National Progress in Meeting the Millennium Development Goals
UNICEF’s country activities
World Health Organisation’s country information
Country profiles of the International Strategy for Disaster Reduction
Water and Sanitation Program Country Fact Files
World Bank country-level Development Indicators
FAO Land and Water country profiles
FAO Specialized Country Profiles and Information Systems