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PROBLEMS AND NEEDS Colorado River Water Quality The Lower Gunnison Basin Unit area contributes about 350,000 tons of salt annually to the Colorado River, which results in an increase of about 37 mg/L at Imperial Dam. As a result of this and other salt sources, the river's water quality has been deteriorating over the long term as riverflows have been developed for man's beneficial use. The Colorado River at its headwaters in the mountains of north- central Colorado has a salinity (dissolved mineral concentration) of only about 50 mg/L. The salinity progressively increases downstream as a result of water diversions and salt contributions from a variety of sources. In 1979, the salinity averaged about 810 mg/L at Imperial Dam, the last major diversion point on the Colorado River in the United States. The high salt load of 10 million tons annually in the Lower Colorado River Basin adversely affects more than 17 million people and about 1 million acres of irrigated farmland in the United States. Municipal and industrial water users and irrigators experience estimated direct and indirect annual economic losses of $450,000 (January 1980 prices) for each increase of 1 mg/L in salinity at Imperial Dam. The salinity also adversely affects water users in Mexico. The losses associated with municipal and industrial use occur pri- marily from increased water treatment costs, accelerated pipe corrosion and appliance wear, increased soap and detergent needs, and decreased drinking water palatability. The Public Health Service recoDDDends that drinking water contain no more than 500 mg/L of total dt;~ivb134 solids (TDS). For irrigators, the high concentrations cause decreased 13