Ensuring poor people’s access to safe drinking-water and adequate sanitation and encouraging personal, domestic and community hygiene will improve the quality of life of millions of individuals. Better managing water resources to reduce the transmission of vector-borne diseases (such as viral diseases carried by mosquitoes) and to make water bodies safe for recreational and other users can save many lives and has extensive direct and indirect economic benefits, from the micro-level of households to the macro-perspective of national economies. The global importance of water, sanitation and hygiene for development, poverty reduction and health is reflected in the United Nations Millennium Declaration, in particular its eight Millennium Development Goals, in the reports of the United Nations Commission on Sustainable Development and at many international fora.

In 2002, the World Health Organization (WHO) published the first scientifically substantiated estimate of the global burden of disease related to water, sanitation and hygiene (3,4). This complemented WHO’s work, in cooperation with the United Nations Children’s Fund (UNICEF), in monitoring the status of and trends in access to both improved drinking-water sources and basic sanitation (5). Subsequently, WHO continued to develop this evidence base for policy and good practice. This has included systematic work on developing an understanding of the impact of interventions on disease incidence and on estimating the costs and benefits of those interventions. The tools being developed by WHO as part of this work are suitable for application at different levels, from local to national to global.

A clear understanding of the burden of disease and the effectiveness of alternative approaches to reduce this burden provides the basis for the development of effective intervention strategies. Estimating the costs and impacts of policy and technical options provides an objective basis from which to inform decision-making-especially important in an area where many different sectors and actors are involved. Understanding how interventions are financed enables us to advocate for their benefits.