Water Safety Plans (WSPs) are a comprehensive risk assessment and management approach to water delivery that were internationally recommended in 2004. WSPs consist of five implementation steps, followed by evaluation. To date, approximately 90 countries have implemented WSPs; however widespread uptake is limited by lack of documented outcomes and impacts. We conducted a systematic review to collate outcomes, impacts, and lessons learned from WSPs developed in general, rural, and three case-study country contexts. Overall, 53 documents met inclusion criteria. In general contexts, the need for institutional support during WSP implementation was highlighted. In rural applications, the need to simplify the WSP process and provide community support was emphasized. In case-study countries, we found the WSP process was selectively adapted and integrated within existing programs. In outcome and impact evaluations, financial outcomes have the clearest evidence base, while operational outcomes are documented most frequently, particularly in relation to infrastructure improvements. However, evidence is lacking on institutional and policy outcomes and impacts of WSPs. To ensure WSPs reach their potential for improving water delivery and management, support should be provided to implementers, outcomes and impacts of urban, peri-urban, and rural WSP implementations should be evaluated, and adaptation of WSPs locally encouraged.