

Figure VI 1—1 — DISPOSITION OF WATER DIVERTED FOR IRRIGATION 



Evapotranspiration 

 from Crop Area 



Evaporation 

 before returning 

 Water Resource 

 Pool 



The diagram shows schematically what becomes of water diverted for irrigation 

 purposes in the U.S. The width of the stream represents the relative quantity of 

 water moving in that path. Water is consumed by evaporation from various sources 

 and evapotranspiration from irrigated areas. This reduces the water supply available 

 for sequential uses. The non-consumptive paths such as seepage, runoff, and perco- 

 lation return water to the resource pool, leaving it available for subsequent uses. 

 This return water may improve or degrade the water quality depending on the initial 

 quality of the water, the uses to which it has been put, and the particular character- 

 istics desired by the sequential users. 



is the technology of water use. Plan- 

 ners have generally assumed a slow 

 increase in per capita water require- 

 ments. It should not, however, be 

 exceptionally difficult to redesign 

 conventional plumbing fixtures and 

 water-using appliances so that water- 

 use rates are reduced without sacrific- 

 ing the amenities of present users. 



The second factor that might sig- 

 nificantly affect domestic consump- 

 tion would be changes in life styles. 

 A shift from dispersed single-family 

 residences to multi-family residences 

 would be the most significant change. 

 Savings in water would be achieved 

 through reduction in lawn and garden 

 water requirements. Changes of this 

 kind are probably closely related 

 to technology through construction 

 costs, transportation techniques, dis- 

 position of leisure time, and public 

 policy with respect to taxation. Sub- 



jects for research on the impact of 

 technology on society in this area are 

 abundant. 



Industrial Water Use — The aver- 

 age values of industrial water use per 

 unit of product produced are ex- 

 tremely large in many industries. 

 There are, however, many opportu- 

 nities for reducing water use by re- 

 cycling, recovery of by-products, and 

 other techniques. Estimates of future 

 industrial use are dependent on esti- 

 mates of future industrial production 

 and the extent to which water- 

 conservation techniques are applied. 



Water in Agriculture — The largest 

 water-using sector in the United 

 States today is irrigated agriculture. 

 In states like California, over 90 

 percent of the water use is for irriga- 

 tion. Future agricultural water re- 

 quirements are therefore extraordi- 



narily important. Unfortunately, they 

 are difficult to assess. What are the 

 future needs for food and fiber 

 production? How much food and 

 fiber will the United States produce 

 for export? How much can food and 

 fiber production in the humid eastern 

 states be expanded? How can water- 

 use efficiency in agriculture be im- 

 proved? What is the possibility of 

 breeding crop types requiring less 

 water or capable of using brackish 

 water instead of fresh water? To what 

 extent will it be possible to raise 

 crops in arid regions in controlled 

 environment chambers? Will exten- 

 sive, low-cost greenhouses in which 

 water use can be carefully controlled 

 become technically feasible? These 

 questions all involve issues of tech- 

 nical feasibility, extent to which 

 efficiency of production can be im- 

 proved, and time-rate at which these 

 developments can be expected. 



Energy Production — The consump- 

 tive water requirements for the pro- 

 duction of electric energy are rela- 

 tively small. A hydroelectric power 

 plant actually consumes only small 

 amounts of water evaporated from 

 the reservoir surface. A thermal plant 

 consumes the water evaporated in 

 cooling the condensers. If predictions 

 that power demands will continue to 

 double every decade (thousand-fold 

 increase in 100 years) prove accurate, 

 however, the current relatively small 

 use will grow rapidly into a major 

 source of water consumption. 



Again, the projection of water re- 

 quirements for power production 

 raises mainly technological issues. 

 What are the prospects for new types 

 of thermal power producers for which 

 cooling- water requirements are less? 

 Are there possibilities of cooling 

 methods that are less demanding on 

 the water resource? Use of heated 

 condenser water for irrigation shows 

 promise of minimizing the "thermal 

 pollution" of streams and improving 

 the efficiency of irrigation. Not all 

 thermal power plants can be situated 

 close to potential irrigated areas, 

 however. What other uses of waste 



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