Water Safety Plans, part of the ‘Framework for Safe Drinking-Water”, emerged from a ten-year WHO process that began in 1994. They turned around the then-dominant focus on ever faster and more specific testing and on treatment-focused actions to secure quality. They demanded re-engagement with understanding and tackling the potential sources of and barriers to contamination, rather than reliance on detecting it once it had occurred. In doing so they increased recognition of the need to intervene in catchment and in distribution as well as treatment to secure reliable water safety. For water suppliers, legislators and regulators they represented a fundamental change, which challenged established ways of working. Such radical change was accepted in large part because of a ten-year process of development that involved 490 people from 90 countries; and more than 50 expert and consultative meetings and processes. The result has been a rate of adoption of this approach that is arguably unprecedented for such a policy initiative. That process of adoption has provided opportunities to understand WSP processes and impacts. High quality studies in Iceland, France and Spain have documented beneficial impacts on water quality, compliance with internal and external standards and on health outcomes. The latter, from a high-income country with good infrastructure and high quality underlying resources is noteworthy. These opportunities have also provided insights into factors that support the successful implementation of Water Safety Plans i.e. what makes them work on-the-ground; and also on the factors associated with their uptake and adoption in policy and regulation. It will contrast the evolution of approaches to and concepts surrounding sanitation safety planning.