Mexico alone pump about 14 billiou gallons a day 

 for this purpose. Pumping of ground water for sup- 

 plemental irrigation in the more humid portion of 

 the country has increased greatly in recent years. 



Most of the water for individual farmstead use 

 comes from wells. Water from deep wells is more 

 apt to be free from pathogenic organisms than 

 that from springs, shallow wells, and surface 

 sources. Because on-farm treatment may be diffi- 

 cult, deep-well water is ordinarily desirable for 

 individual farmsteads unless dissolved solids are 

 excessive. 



A dependable source of livestock water of good 

 quality is necessary for the profitable production 

 of animals. 



Problems of agricultural water quality 



Because the factories of agriculture are living 

 things, water quality affects not only the end prod- 

 uct, but also the efficiency of the production 

 machinery. Livestock, ill because of waterborne 

 disease or excess minerals, and irrigated crops 

 suffering from high salinity of irrigation water are 

 inefficient tools of production. 



Agriculture, like any other industry or activity 

 of man, must deal with the quality-lowering impact 

 of all man's activities on water. Excessive quanti- 

 ties of silt from agricultural activities, road con- 

 struction, and urban development plague many of 

 our streams. Pollution from sewage, domestic and 

 industrial, continues to add each year to the water 

 quality problems of the farmer and urban dweller. 

 Upstream irrigation, reservoir evaporation, and 

 lowering or recycling of ground water impose in- 

 creasingly difficult problems for downstream irri- 

 gators because of increased salt concentrations. 



Effects of water quality deterioration or the im- 

 pact of low-quality supplies on agriculture are 

 commonly insidious rather than dramatic. Even 

 relatively small-scale changes may result in large 

 economic consequences because of the sheer size 

 of the activity involved. 



Excess salinity has been the instrument of de- 

 struction of profitable irrigation from the earliest 

 history of man. Besides the common ions, trace 

 elements in small concentrations, such as boron, 

 may be extremely harmful; and in many areas of 

 the world, pollution of water supplies by un- 

 treated or inadequately treated sewage in irrigation 

 results in widespread diffusion of enteric diseases. 



While a great deal is known about the inhibiting 

 effects of salinity on plant growth, only very pre- 

 liminary assessments have been made of the eco- 



nomic consequences in terms of the cost of reduc- 

 ing salinity. Thome and Peterson (166) estimate 

 that approximately 1.35 billion acre feet of river 

 flow in the United States each year carries to the 

 sea between 250 and 330 million tons of salt. This 

 reflects a continuing geological process, which, in 

 total, man may not have changed greatly. But in 

 many places man's activities have made local 

 changes of great importance in the vast process. 

 For example, the total flow ot salt down the Colo- 

 rado River system may not be much greater than 

 it was 100 years ago, but the amount of water 

 transporting the salt has decreased appreciably, 

 thus raising the salt concentration. 



Besides direct pollution, management of water 

 resources may result in indirect environmental 

 consequences. Improper irrigation practices may 

 provide favorable environments for vectors of 

 disease, such as mosquitoes for malaria or en- 

 cephalitis, or snails in schistosomiasis (fortunately, 

 the latter is not prevalent in the United States at 

 the present time). Other aspects of irrigation 

 water resource management include control of 

 weed seeds and insect pests. 



Very little attention has been given to the opti- 

 mum quality of drinking water for farm animals. 

 While the standards of quality for human con- 

 sumption may not be justified here, this could be a 

 desirable goal because such waters often also serve 

 other uses on the farmstead. There are certain 

 contaminants which may be hazardous to live- 

 stock. The danger of direct infection to livestock 

 through the consumption of water contaminated 

 with pathogenic agents is definite and deserves 

 attention. 



Private farm systems provide water for drinking 

 purposes, food preparation, laundry, bathing, and 

 preparation of products for marketing. Many farms 

 rely on springs or shallow wells for their water 

 supplies and such supplies may be contaminated. 

 Both the farmer and consuming public benefit 

 from the use of good quality water. 



Dairy farming requires large quantities of water 

 for cooling and for washing milk-handling equip- 

 ment. This must be of drinking water quality even 

 though other uses may not require this degree of 

 purity. 



The multiple uses of water in agriculture require 

 that streams and other irrigation supplies be of 

 such quality that potable water can be produced 

 economically on the farm and without serious 

 fluctuations in quality. Furthermore, raw water 

 supplies should be satisfactory usuaUy without 

 treatment, for irrigation of vegetable and fruit 

 crops. The frequency and accuracy of monitoring 

 farm water supply sources should depend in part 



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