Figure 18—Thermoelectric cooling is expected to be the most important source of demand for 
water withdrawals. (Photo courtesy of USDA Soil Conservation Service.) 
Irrigation 
Irrigation—the act of applying water to 
land to promote the growth of 
vegetation—covers a multitude of uses 
from watering agricultural crops to golf 
courses to home lawns and gardens. 
Irrigation water comes from wells, 
surface sources on the site, and surface 
sources provided by offsite suppliers 
such as irrigation districts and ditch 
companies. Irrigation withdrawals in 
1985 totaled 142.5 billion gallons per 
day, with 40 percent originating from 
wells and 60 percent from surface 
sources. Three of every four gallons 
from surface sources are provided by 
offsite suppliers. Irrigators in the Great 
Plains rely most heavily on ground- 
water withdrawals; those in other parts 
of the Rocky Mountain and Pacific 
coast regions rely most heavily on off- 
farm suppliers. 
Because both wells and onfarm 
surface-water sources must be pumped 
to deliver water to crops, the energy 
expenses of irrigating farmland can be 
large and have a major impact on the 
extent of irrigation. During the past 
decade of high energy prices, for 
example, irrigated farmland acreage 
fell by 11 percent. Decreased export 
demands and lower commodity prices 
also contributed to reduced use of 
irrigation for agriculture. 
About half of the withdrawals for 
irrigation are consumed. Irrigation is 
the largest consumptive user by far, 
accounting for 73.8 billion gallons per 
day—79 percent of the total 
consumption of water for all uses (fig. 
19). Thus, of all the uses, the outlook 
for water used as irrigation will have 
the most influence on the overall 
demand-supply outlook for water. 
Irrigation water usage is projected to 
grow at a much slower rate over the 
next 50 years than over the previous 25 
years. Irrigation is expected to remain 
important, however, in all regions 
except the North. The primary reasons 
for expecting this slowdown are higher 
pumping costs and the potential of 
technology for conserving water used 
in irrigation. The expected increases in 
energy costs in the future will increase 
pumping costs, thereby reducing the 
returns per acre from irrigation and 
forcing some acreage into dry-land 
crop production. Competition from 
higher value uses and lack of additional 
water supplies will also be important in 
raising irrigation costs. Increased water 
costs may provide market incentives 
for adoption of existing water-saving 
technologies such as drip or trickle 
irrigation systems. 
Other Water Uses 
The remaining water uses are 
municipal central supplies, industrial 
self-supplies, domestic self-supplies, 
and livestock watering.2 In total, they 
accounted for 16.7 percent of 
consumption and 20.6 percent of 
withdrawals in 1985. Each of these 
uses 1s expected to grow in the future, 
and by 2040, they collectively account 
for 19.6 percent of consumption and 
23.7 percent of withdrawals. 
Trends and projections in withdrawals 
and consumption for each of the other 
uses are In appendix tables 6 and 8. 
? The term “municipal central supplies” refers to 
water withdrawn by public or private water- 
supply utilities that distribute treated water 
through a network of pipes to household, 
commercial, and industrial users. Self-supplied 
industrial water use is defined in this Assessment 
as water withdrawn and consumed by industries 
for their own use, other than cooling 
thermoelectric power plants. Water for domestic 
self-supplies includes water for household 
consumption, drinking water for livestock and 
other uses such as dairy sanitation, evaporation 
from stock-watering ponds, cleaning, and waste 
disposal. Livestock watering includes water 
provided for drinking by livestock and water 
used to maintain sanitary living conditions for 
livestock. 
19 
