Peak water is a term coined to describe the risk of developing water scarcity as a result of unsustainable uses of water supplies. This is a particular concern in hot, dry areas where water supplies are already limited and people may be moving into the area, putting more strain on water availability. While it is not possible to run out of freshwater altogether, in some communities water use is outstripping availability, creating environmental and social problems. This term attracted public attention in 2010 as the result of a study published by hydrologist Peter Gleick discussing the issue of sustainable water use and peak water.
Gleick defines three types of peak water, looking at different environmental and social concerns surrounding water usage. The first is renewable peak water, referring to the use of renewable water resources like rivers, lakes, and streams. These should theoretically recharge as a result of rainfall and snow melt, as long as communities do not overextract these resources, draining rivers and lakes dry. Some communities in regions like the American Southwest have already hit this limit.
Another form is nonrenewable peak water, looking at exploitation of resources like underground aquifers. These take centuries to develop, and if they are drained, they will not refill for many more centuries. Regions relying on such resources can hit their limits and find that no more water is available, even as residents demand more water for uses like bathing, cooking, and irrigation. Other resources may become polluted, creating a situation where freshwater is present, but not usable.
Ecological peak water is the balance point where human uses of water start to cause environmental problems, contributing more harm than benefits. In this case, while more water may be available, it would not be sustainable to tap into those resources, as they may be needed for other things, like sustaining plant and animal populations. Using too much water can contribute to the development of desertification and other environmental issues.
Balancing the human needs for water with ecological issues can be complicated. Negotiations over water rights often become contentious, since water resources often sprawl across multiple borders. The actions of residents of one region can have an impact on others, or two communities may need to share the same resource and can have trouble doing so equitably. Reducing water usage through conservation measures is an important part of addressing peak water, but as human populations grow, this becomes more challenging.