Chapter 3 of the Water, ice, society, and ecosystems in the HKH (HI-WISE) assessment report investigates the state of knowledge about the quality and quantity of climatic drivers, water resources, and their implications for present and future hydrological regimes. It also looks at water-related hazards and notes the most significant impacts recorded. Climate change is projected to cause significant changes in the HKH cryosphere and impact the region’s hydrological cycle and overall water availability. Mid-century will see ‘peak water’ reached in most HKH river basins. Water availability is expected to decrease, although future water availability is hard to accurately predict. Cascading slow and fast-onset hazards are likely to confound early warning and adaptation measures. There is strong evidence that glacier retreat and rise in rainfall will drive hazards.