Water is essential for economic growth, human health, and the environment. Yet governments around the world face significant challenges in managing their water resources effectively. The problems are multiple and complex: billions of people are still without access to safe water and adequate sanitation; competition for water is increasing among the different uses and users; and major investment is required to maintain and improve water infrastructure in OECD and non-OECD countries. This OECD series on water provides policy analysis and guidance on the economic, financial and governance aspects of water resources management. These aspects generally lie at the heart of the water problem and hold the key to unlocking the policy puzzle. Executive summary : Chapter 1. Framing the water reform challenge; Key water trends and projections; Emerging issues in water policy; Designing reforms that are realistic and politically acceptable; Chapter 2. Meeting the water financing challenge; What are the benefits from investing in water and sanitation?; How much investment is needed?; Closing the financing gap; Bridging the financing gap: Tapping repayable sources of funding; The role of the private sector to help mobilise financing; Beyond water and sanitation: Financing water resources management; Moving forward on the water financing challenge; Chapter 3. Meeting the water governance challenge; A multi-level governance approach for addressing complexity in the water sector; Observations from the institutional mapping of roles and responsibilities in the water sector; Challenges to coordinating water policies across ministries and between levels of government; Governance fragmentation at the metropolitan level; Multi-level Co-ordination of Water Policies; Moving forward on meeting the water governance challenge; Chapter 4. Meeting the water coherence challenge; Framing the coherence challenges; Linkages between energy, water and the environment; Linkages between agriculture, water and the environment; Moving forward on the water, energy and agriculture coherence challenge