Regulations play a fundamental role in achieving public policy objectives, including the protection of human health and the environment, the fight against monopolies, or the efficient provision of water and sanitation services. Regulatory impact assessment (RIA) is an important tool for ensuring that regulations are of good quality. This report provides guidance for implementing RIA at the National Superintendence of Sanitation Services in Peru (Sunass). After assessing the agency’s process for issuing rules, the report provides recommendations for designing legal reforms needed to establish RIA as a permanent practice as well as training for the staff who will develop the RIAs. The report includes technical guidelines on undertaking public consultation, identifying public policy problems, and performing cost-benefit analysis.