This Analytical Brief provides information about past assessments, outlines the challenge but also provides a plan for a world water quality assessment, which, if undertaken, would provide decision makers with the information they need to address this challenge. The Analytical Brief also explores the strong linkages between water quality and the Sustainable Development Goals (SDGs). SDG 6, “Ensure availability and sustainable management of water and sanitation for all,” includes a speci c target (6.3) dedicated to water quality. Central questions include: ‘how can the water quality target be achieved?’; ‘How will worsening water pollution affect SDGs for health, food security, and biodiversity, among others?’; Or, conversely, ‘how can actions to protect and enhance water quality help meet other SDGs?’.