introduction 



ration for sale. Particularly critical is the use of 

 water in the production of market milk where 

 clean, bacteriologically safe water is mandatory. 

 In addition, the current time lag between milk 

 production on the farm and use in the home re- 

 quires the control of psychrophiles which adversely 

 affect milk quality. 



The purity of water consumed by livestock has 

 far-reaching implications; polluted water can cause 

 death or disease of livestock and contaminate ani- 

 mal products. Many pollutants are important to 

 the livestock industry. Some understanding of the 

 tolerance level of these in water is important even 

 though animals also inevitably acquire organisms 

 and contaminants from soils or feeding and water- 

 ing locations. A dependable source of livestock 

 water of good quality is necessary for the profitable 

 production of animals. 



Irrigation is the largest, single-purpose beneficial 

 consumptive use of water in agriculture. Water 

 quality criteria for irrigation become more critical 

 as fuller use is made of both available water and 

 irrigable land. Early irrigation developments were 

 largely on streams where only a small part of the 

 annual flow was used. Such streams contained 

 mainly dissolved solids resulting from the normal 

 leaching and weathering processes. Additional 

 uses concentrated the dissolved solids and intro- 

 duced other chemical and microbiological pol- 

 lutants that have become potentially hazardous to 

 crops, livestock, and to man. 



Sources of water for agriculture 



AMERICAN AGRICULTURE is both a 

 modem industry and a way of life. Not only 

 does water quality affect the safety and value of its 

 products, but also the health and welfare of farm- 

 ers and their families. Farmers do not usually have 

 access to the large, weU-controlled water supply 

 and waste disposal systems of the great munici- 

 palities. 



The Subcommittee on Water Quality for Agri- 

 cultural Uses is concerned with water used on indi- 

 vidual farmsteads, for livestock, and for irrigation 

 of crops. 



For farmstead waters, particular attention is 

 given to the use of water by the human farm popu- 

 lation for drinking, food preparation, bathing, and 

 laimdry. Other important uses include washing 

 and hydrocooling of fruits and vegetables in prepa- 



Other than from precipitation, about three- 

 fourths of the water used in agriculture comes 

 from surface supplies and one-fourth from wells 

 and springs. 



Man has been able to make better use of the 

 water by constructing dams, reservoirs, and dis- 

 tribution systems. During the period of greatest 

 need for irrigation and livestock, streamflows are 

 often minimal or even nonexistent. The highly 

 productive irrigated areas of the West have water 

 available because of the very large investment in 

 dams, reservoirs, and water charmels. 



Another large segment of land is irrigated by 

 pumping water from the ground. The total usable 

 underground water supply has been estimated to 

 be equivalent to 10-year's total rainfall or 35-year 

 runoff (172). Underground waters supply more 

 than 20 billion gallons of water a day for irrigation. 

 The States of California, Arizona, Texas, and New 



112 



