<P> Successful agriculture is dependent upon farmers having sufficient access to water . However, water scarcity is already a critical constraint to farming in many parts of the world . With regards to agriculture, the World Bank targets food production and water management as an increasingly global issue that is fostering a growing debate . Physical water scarcity is where there is not enough water to meet all demands, including that needed for ecosystems to function effectively . Arid regions frequently suffer from physical water scarcity . It also occurs where water seems abundant but where resources are over-committed . This can happen where there is overdevelopment of hydraulic infrastructure, usually for irrigation . Symptoms of physical water scarcity include environmental degradation and declining groundwater . Economic scarcity, meanwhile, is caused by a lack of investment in water or insufficient human capacity to satisfy the demand for water . Symptoms of economic water scarcity include a lack of infrastructure, with people often having to fetch water from rivers for domestic and agricultural uses . Some 2.8 billion people currently live in water - scarce areas . </P> <P> Irrigation schemes involve solving numerous engineering and economic problems while minimizing negative environmental impact . </P> <Ul> <Li> Competition for surface water rights . </Li> <Li> Overdrafting (depletion) of underground aquifers . In the mid-20th century, the advent of diesel and electric motors led to systems that could pump groundwater out of major aquifers faster than drainage basins could refill them . This can lead to permanent loss of aquifer capacity, decreased water quality, ground subsidence, and other problems . The future of food production in such areas as the North China Plain, the Punjab, and the Great Plains of the US is threatened by this phenomenon . </Li> <Li> Ground subsidence (e.g. New Orleans, Louisiana) </Li> <Li> Underirrigation or irrigation giving only just enough water for the plant (e.g. in drip line irrigation) gives poor soil salinity control which leads to increased soil salinity with consequent buildup of toxic salts on soil surface in areas with high evaporation . This requires either leaching to remove these salts and a method of drainage to carry the salts away . When using drip lines, the leaching is best done regularly at certain intervals (with only a slight excess of water), so that the salt is flushed back under the plant's roots . </Li> <Li> Overirrigation because of poor distribution uniformity or management wastes water, chemicals, and may lead to water pollution . </Li> <Li> Deep drainage (from over-irrigation) may result in rising water tables which in some instances will lead to problems of irrigation salinity requiring watertable control by some form of subsurface land drainage . </Li> <Li> Irrigation with saline or high - sodium water may damage soil structure owing to the formation of alkaline soil </Li> <Li> Clogging of filters: It is mostly algae that clog filters, drip installations and nozzles . UV and ultrasonic method can be used for algae control in irrigation systems . </Li> </Ul> <Li> Competition for surface water rights . </Li>

Lever system of irrigating fields is also referred to as