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. .) . ~.. o "'-l IV EFFECTS OF SALINITY ON WATER USE (continued) In contrast to the Upper Basin, the quality of the water supply at most points in the Lower Basin does not meet the Public Health Service recom- mended limits of 500 mg/L for total dissolved solids. Mineralized water supplies with salinity concentrations in the range of those values observed in the Colorado River, however, are commonly accepted in the southwestern United States, with little detriment to the potability of the supply. The use of this mineralized supply imposes an increased treatment cost as hardness level. are high enough that water softening is desirable in addition to normal treatment. Another means of reducing the problem is by mixing better quality water with the saline water. This solution is limited to those areas having other supplies and is an additional cost. E. Economic Impacts A consortium of water resources centers in the states of Arizona, California, Colorado, and Utah cooperated in a study funded by the Office of Water Research and Technology and the Water and Power Resources Service to assess the economic damages caused by various salt concentrations to agricultural and municipal water users. This study is documented in a report, "Salinity Management Options for the Colorado River," Water ReRources Planning Series Report P-78-003, June 1978. Based upon the findings of that report, the Water and Power Resources Service has published a summary working document entitled, "Colorado River Salinity Economic Impacts on Agricultural, Municipal, and Industrial Users." It is estimated that the annual damages to the Lower Basin water users in 1976 dollars are $343,000 for each rise of one mg/L in salinity concentration at Imperial Dam. This damage figure is approximately $450,000 in 1980 dollars. These annual damage costs per mg/L were calcu- lated using the 1972 salinity standard of 879 mg/L (approved by EPA in 1975) and a projected full development salinity level of 1225 mg/L. In 1976 dollars the $343,000 annual damages are divided as follows: 'lIunicipal; Metropolitan \olater District $187,000, Central Arizona Project $26,300, and Lower Main Stem users $27,200, the total agriculture annual damages are $102.500. Industrial damages are considered relatively small and diffult to identify. Presently industrial costs are included in the municipal. Iq/<6 1b - ~ 34 :'.000/ rVI c;j/ e. 36