Climate change is real, and taking prudent measures to plan for and adapt to climate change must become an integral part of the Bank's water practice. There is now ample evidence that increased hydrologic variability and change in climate has and will continue have a profound impact on the water sector through the hydrologic cycle, water availability, water demand, and water allocation at the global, regional, basin, and local levels. This report and the analytical work leading to it are focused on key topics related to the impact of climate change on the water cycle and water investments. This report contributes to the World Bank agenda on climate change and more specifically, informs the water sector investments on climate issues and climate-smart adaptation options. Using the existing knowledge and additional analysis commissioned. The report illustrates that climate change is affecting the hydrologic cycle and the projected future hydrology will have a direct impact on the water resources base availability, usage, and management. Depending on the type of the water investment, this impact can be positive, negative, or neutral. The report addresses the stress on and vulnerability of the water systems through use of reliability, resilience, and robustness as the key indicators of sensitivity of water systems for climate induced failure. Current practices in the sector are examined in order to better understand the state-of-the-science for incorporating current and future variability