Water is a critical natural resource and an essential service. It is central to the attainment of nearly all the Sustainable Development Goals (SDGs). Water security is crucial for countries to meet long-term development objectives in the current context of climate change, ensuring the protection of vulnerable populations, infrastructure assets, and agricultural, energy, and industrial production. The transboundary nature of water resources resembles the characteristics of global public goods, necessitating coordinated international action. However, water resources are under severe stress and water services delivery is deficient on account of underinvestment in the sector. Closing the investment gap requires a combination of public, concessional, and private sources of finance, which are directed to meeting key sector goals, while optimizing the contributions of both the public and the private sector.