The performance of water and sanitation utility companies varies greatly, but many are underperforming. This is due mainly to systemic issues, which can include weak governance, lack of accountability, poor management, inadequate or aging infrastructure, and insufficient funds for operations and maintenance. In many cases the public sector water and sanitation service providers seek support to overcome the challenges. Public-private partnerships (PPPs) can be an important option for implementing sector reform strategies and can address the key challenges to providing universal and sustainable service access. As a partner, the private sector can bring technical and management skills and experience, commercial discipline, and private finance to help tackle such challenges in a structured and contractually binding manner. The objective of this guidance note is to offer practical, experience-based guidance to those considering or currently engaging in PPP in the water sector, and to provide a basic understanding of water PPPs and the PPP cycle to better inform dialogue with governments that are considering PPP arrangements. It builds on the experience of water and sanitation program (WSP) in supporting PPP reforms in developing countries, especially through the domestic private sector. This note outlines a rationale and approach for launching a water sector PPP so that government leaders and private sector providers can have informed discussions about the path forward should they choose to explore this approach in their countries.