Water, sanitation and hygiene (WASH) are essential for both human survival and sustainable development. In this article for the United Nations Association of the UK, Beatrice Mosello and Mariana Matoso argue that for guaranteeing WASH for all, we know what we need to do, who needs to do it and what the costs of failure are. So what are the obstacles, and how we can ensure that everyone has access to these basic necessities? They propose solutions at the institutional, accountability-based and financial levels to ensure that we reach the ambitious targets set out in sustainable development goal 6, the water goal.