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For the tributaries the dissolved solids concentration and character varied from the headwaters down stream. Eagle River at Gypsum had a concen- tration of 293 p.p.m. with sulfate and chloride higher than in the Colorado River above the Eagle. The Gunnison at Grand Junction had a concentration of 709 p.p.m. with sulfate the principal acidic constituent. Dolores River at Gateway, Colorado, had a concentration of 507 p.p.m., with appreciable proportions of sulfate and chloride. These'tributaries are responsible to some extent for the increase between Cameo and Cisco. Green River had a concentration of 306 p.p.m. at Jensen, Utah I considerably lower than that of the Colorado. There is increase downstream in dissolved solids of the Green River, but at its mouth the concentration is lower than that of the Colorado. San Rafael River, tributary to the Green, is of high concentra. tion, having had 1,870 p.p.m. in February 1948, with sulfate the principal constituent. The San Rafael is so small in proportion to the Green that it has little effect. The San Juan brings in appreciable quantities of water and large quantities of sediment, but the chemical qU:ality is good, the average dis- solved solids content being 339 p.p.m. The' Bill Williams brings in rela- tively small quantities of moderately mineralized water, but with a rather high sodium percentage. The Gila at Solomonsville, 528 p.p.m.,is relatively high in chloride, which can be attributed in part to salt springs in the San Francisco drainage basin. The average values given represent pretty well the quality of the water that would be available in a reservoir if the entire annual flow were caught, well mixed, and if nothing else happened. The analyses for Grand Canyon and Hoover Dam show that some things do happen during storage. The increase of more than 100 p.p.m. is evidenqe of changes that take place in Lake Mead. Evaporation losses from Lake Mead are about 750,000 acre-feet a year. The dissolved solids of this evaporated water are left in the reservoir. There is precipitation of Chemical compounds in the lake. The white deposit along the shore line consists chiefly of silica and calcium carbonate. During the first fourteen year$ of storage about 1,000,000 tons of silica and 9,000,000 tons of calcium ca~bonate were precipitated in the lake. Also soluble salts in part of the reservoir area have been dissolved. In the fourteen years of storage there was;a net gain of about 20,000,000 tons of dissolved solids, chiefly sulfate,: chloride, calcium and sodium. Records indicate that the rate of solution'has decreased, because the more easily soluble beds have been dissolved and some covered with sediment. It seems certain that the maximum increase in dissolved solids in Lake Mead has been experienced. The volume of water draining irri~ated areas may be low, but the dissolved solids content of the drainage waters is usually high and will have an appreciable effect on the quality of the main stream. This effect is very noticeable where the water is used several times, as in the Salt River Valley. It is not safe to make a general statement concerning quality conditions in the Salt River Valley except' that they are not good and need detailed study. Water at the head of the Gillespie Canal in May 1945 had a dissolved solids concentration of 4,070 p.p.m. and a sodium percentage of 67. Standards of water quality are not too well fixed. The U. S. Public Health Service has set up standards for water to be used in interstate car- riers, but those standards are not applicable at this time to most uses in -18.