Fresh water sources. Cutaway illustration of sources of fresh water use by humans, mostly living in cities (far left). Fresh water falls as rain and snow over mountains (upper right). Around 1 percent enters lakes and rivers, and is harnessed by dams, reservoirs and irrigation canals (centre and lower left). 69 percent is locked in ice (top right) and the remaining 30 percent is groundwater (shown in cutaway at lower left), extracted by deep wells for agriculture. Groundwater is used during droughts, but overuse means that reserves are shrinking. Dashed cloud outlines show predicted precipitation changes (more rain and less snow) as the Earth’s climate warms.