<P> Recreational usage may reduce the availability of water for other users at specific times and places . For example, water retained in a reservoir to allow boating in the late summer is not available to farmers during the spring planting season . Water released for whitewater rafting may not be available for hydroelectric generation during the time of peak electrical demand . </P> <P> Explicit environment water use is also a very small but growing percentage of total water use . Environmental water may include water stored in impoundments and released for environmental purposes (held environmental water), but more often is water retained in waterways through regulatory limits of abstraction . Environmental water usage includes watering of natural or artificial wetlands, artificial lakes intended to create wildlife habitat, fish ladders, and water releases from reservoirs timed to help fish spawn, or to restore more natural flow regimes </P> <P> Like recreational usage, environmental usage is non-consumptive but may reduce the availability of water for other users at specific times and places . For example, water release from a reservoir to help fish spawn may not be available to farms upstream, and water retained in a river to maintain waterway health would not be available to water abstractors downstream . </P> <P> The concept of water stress is relatively simple: According to the World Business Council for Sustainable Development, it applies to situations where there is not enough water for all uses, whether agricultural, industrial or domestic . Defining thresholds for stress in terms of available water per capita is more complex, however, entailing assumptions about water use and its efficiency . Nevertheless, it has been proposed that when annual per capita renewable freshwater availability is less than 1,700 cubic meters, countries begin to experience periodic or regular water stress . Below 1,000 cubic meters, water scarcity begins to hamper economic development and human health and well - being . </P>

What are the three main sources of water