Unsafe water, lack of sanitation and adequate hygiene contribute to the leading killers of children under five, including diarrhoeal diseases, pneumonia and undernutrition, and have implications on whether or not children - especially girls - attend school. Thus, achieving Millennium Development Goal 7, and its 2015 targets of reducing by half the proportion of people without sustainable access to safe drinking water and basic sanitation, is of vital relevance for children and for improving nutrition, education and women's status. This issue of Progress for Children reports on whether the world is on course to reach MDG 7, and where efforts are falling short.