nology that will permit more water recycling to 

 meet environmental standards. Projected manufac- 

 turing withdrawals show the greatest rate of decline 

 in the 1975-2000 period, falling 61 percent from 

 51 billion gallons per day to 19.7 billion gallons 

 per day; after 2000 some increase is expected. 



Contrary to the overall declining trend, withdrawals 

 for domestic and commercial uses and mineral extrac- 

 tion are expected to increase moderately. 



Water Withdrawals by Region and Use 



Total water withdrawals by water resource region 

 are shown in table 7.2. Current and projected with- 

 drawals for each region reflect both the relative 

 availability of water and the uses that are most 

 common in the region. For example, irrigation is 

 the major withdrawal use nationwide, but it is of 

 little importance in humid regions where precipitation 

 is distributed throughout the year, such as in the 

 New England and Ohio regions. Similarly, with- 

 drawals for steam electric cooling are relatively low in 

 the Columbia-North Pacific region, which is- heavily 

 dependent on hydroelectric power at the present time. 



Total withdrawals are now greatest in the Great 

 Lakes, Ohio, Missouri, Columbia-North Pacific, and 

 California-South regions. For the first two regions, 

 totals reflect the importance of fossil-fueled steam 

 generating systems and a concentration of manufac- 

 turing activities (tables 7.4 and 7.5); for the other 

 three regions, withdrawals for irrigation are by far the 

 most important (table 7.3). The latter three regions 

 together account for more than 60 percent of all 

 irrigation withdrawals in the United States. 



Withdrawals for irrigation are expected to continue 

 to increase over the next 10 years, but eventually 

 will decline because of the adoption of water- 

 conserving techniques such as drip irrigation and 

 channel lining. For the Missouri, California, and 

 Pacific Northwest regions, the proportion of total 

 withdrawals is expected to increase from 60 percent 

 to 66 percent, but the overall regional pattern of 

 water use for irrigation is not likely to change 

 drastically. 



Steam electric generation currently accounts for 

 about 22 percent of total water withdrawals (fig. 

 7.2). This rate will probably decrease to about 19 

 percent or 80 billion gallons a day by 2000. The 

 largest withdrawals for power cooling in 1975 were 

 in the South Atlantic Gulf, Great Lakes, and Ohio 

 regions, which accounted for about 65 percent of 

 the withdrawals for that purpose (table 7.4). 



Because of the expected adoption of new cooling 

 technology, several regions including the Great Lakes 

 and Ohio will experience significant declines in with- 



drawal use in future years. Significant withdrawal 

 increases are expected in the Lower Mississippi and 

 Texas Gulf regions. 



Water withdrawals for manufacturing will decline 

 from 51 to 20 billion gallons a day from 1975 

 to 2000, largely because of increased use of recycling 

 in response to water pollution regulations (table 7.4). 

 The Great Lakes and Ohio regions were the largest 

 users of manufacturing water in 1975 (47 percent), 

 but their part in manufacturing withdrawals is 

 expected to decline to about 24 percent of the total 

 in 2000, with the South Atlantic Gulf and Texas 

 Gulf becoming more significant (table 7.5). 



Domestic and commercial use was the next largest 

 withdrawal user, accounting for 8 percent of all 

 withdrawals in 1975 (tables 7.6 through 7.8). This 

 use is expected to increase to about 12 percent 

 of the total by 2000, surpassing manufacturing as 

 the third largest withdrawal user. The regional dis- 

 tribution of residential and commercial users is related 

 closely to population density, which is not expected 

 to change much in the next 25 years. 



The remaining uses, including minerals production 

 and public land administration, account for less than 

 3 percent of total withdrawal use. Although they are 

 not the major users in any water resource region, 

 their current and potential importance in many local 

 areas may be great, especially where water supplies 

 are limited. 



Consumptive Use of Water 



Much of the water withdrawn for most uses is 

 returned to a water source for reuse. For example, 

 of 51 billion gallons a day withdrawn for manu- 

 facturing in 1975, about 45 million gallons a day 

 were returned for reuse. On the other hand, irri- 

 gation consumes, through transpiration and evapor- 

 ation, over one-half (54 percent in 1975) of the total 

 water withdrawn for that purpose. Consumptive use 

 of water is generally considered more critical than 

 water withdrawal because it represents an absolute 

 reduction in available water supply. Once used con- 

 sumptively, water is not available for reuse until 

 it completes its passage through the phases of the 

 hydrologic cycle to return to earth in some form 

 of precipitation. 



The greatest consumptive use of water in the United 

 States in 1975 was for irrigation which accounted 

 for 81 percent of the total (table 7.9 and fig. 7.3). 

 Manufacturing and domestic central supplies ac- 

 counted for another 10 percent, with the remaining 

 9 percent about equally divided among the other 

 uses. Trends in consumptive use are considerably 

 different from those for withdrawals. Without excep- 

 tion, all consumptive uses are expected to increase in 



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