Farmstead water supplies 



In view of the wide variety of sources used 

 for farmstead water supplies and uncontrolled 

 influences of geographic location and climatic 

 conditions, no single set of values can realistically 

 be established as criteria for farmstead supplies 

 and accordingly most of the values are given in the 

 form of acceptable ranges at point of use. In de- 

 veloping the criteria summarized in table IV-1, 

 considerable reliance has been placed on the U.S. 

 Public Health Service Drinking Water Standards. 

 Water which meets these standards is generally 

 safe and acceptable to the user. Farmstead water 

 supply includes water to be used for all house- 

 hold purposes, washing of raw agricultural com- 

 modities, and for milk sanitation. Specific require- 

 ments above those for general farmstead use are 

 indicated also. This summary should be used only 

 in conjunction with the text of this report and 

 appropriate references. See table IV-1, below. 



Livestock water supplies 



Available literature on various substances which 

 occur as contaminants of drinking water for live- 

 stock has been reviewed. Such contaminants in- 

 clude inorganic elements and their salts, organic 

 wastes and mill effluents, pathogens and parasitic 

 organisms, herbicide and pesticide residues, and 

 radionuclides. Important and significant variables, 

 including nature and intake of dietary dry matter, 

 species, age and productivity of animals, and in- 

 terrelationships among the contaminating ingre- 

 dients, make establishment of a single set of water 

 purity values for livestock unfeasible. The relation- 

 ship of water intake to total dietary intake by live- 

 stock is of particular significance. For example, 

 much lower levels of a toxic contaminant should 

 be set for water if the dry feed to be ingested is 

 unavoidably high in the same substance. In gen- 

 eral, the risk of toxicity is less from water than 

 from feed sources. 



Employment of biological indicators, such as 

 fish, in livestock water supplies is proposed as a 

 means of monitoring their safety from the stand- 

 point of chemical toxicity. Fish do not, however, 

 normally indicate presence of pathogenic orga- 

 nisms with sufficient sensitivity to protect livestock 

 from these contaminants. 



Animal pathogens may occasionally enter into 

 a water cycle and management of water resources 

 can materially influence distribution of some 

 diseases. The involvement of the water supply in 



such cases should be supported by epidemiological 

 studies in addition to presumptive or definitive iso- 

 lation from the water environment. Danger from 

 certain microbiological pathogens may be in- 

 creased in situations where water supplies are 

 alkaline. 



In some instances, water quality standards are 

 set in conformity with accepted residual levels in 

 marketable animal tissues or products rather than 

 in relation to any demonstrable toxic effect upon 

 the animal themselves. 



Irrigation water supplies 



Variations and interactions of soils, plants, 

 water, and climate preclude the establishment of a 

 single set of criteria to evaluate all water quality 

 characteristics for irrigation purposes. It is the 

 intent of this report to list tentative criteria where 

 possible and to suggest guidelines where specific 

 criteria cannot be defined. These recommenda- 

 tions are subject to revision as more knowledge 

 accumulates. 



The following summary of criteria should be 

 used in conjunction with references to the text of 

 the report as noted. 



Salinity 



ARID AND SEMIARID REGIONS 



Table IV-3 of recommended criteria for salin- 

 ity or total dissolved solids (TDS) assumes that 

 related factors set forth in this report are taken 

 into consideration. This includes good irrigation 

 practices and soil and plant variables (pp. 167- 

 171). 



HUMID REGIONS 



Where irrigation is practical in humid areas, it 

 is unlikely that any great accumulations of salt will 

 occur over a period of time. For this reason, cri- 

 teria suggested above for arid regions may be sig- 

 nificantly increased for humid regions. More ap- 

 propriate criteria are indicated in pages 173-174. 



SAR and Sodium 



Water having sodium adsorption ratio (SAR) 

 values between 8 and 18 may have an adverse 

 effect on the permeability of soils containing an 

 appreciable proportion of clay because its use 

 causes undesirable amounts of sodium to be ad- 

 sorbed. Where used on sensitive crops, SAR val- 



115 



