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o ,-, ..- w <.0 ., .' 1.' frequent bacteriological examination, subs~antially free from color and turbidity, and of satisfactory chemical quality. Harmful chemical con- stituents such as lead, selenium, arsenic, and hexavalent chromium are not normally present in natural waters but are introduced only as 'pollutants from industrial processes. Other harmful chemical constituents such as fluorides and nitrates are found more frequenUy in natural waters. These chemical agents should not be present in water supplies to exceed the stan- dards recommended by the U. S. Public Health Service. For detailed standards and characteristics of acceptable water supplies, see the Public Health Ser- vice Drinking Water Standards (1946) (Reprint No. 2697 from the Public Health Reports, Vol. 61, No. 11, March 15, 1946, Pages 371-)84, see Appendix). In some instances the standards and recommendations of the Public Health Service can be met with chlorination as a minimum of treatment. In other cases, ex- tensive treatment is required. The advantages in us1Dg wells as the source of water have lODg been recognized. Where ground water is available in the required amount and quality, it generally can be developed quickly and at a relatively low cost. Ground water from deep-seated spriDgs or from wells seldom shows changes in quality such as occur in surface water. In some cases, however, quality changes may occur as a result of leakage through defective well casiDgs. The quality of water obtained from wells usually changes with variations in the depths from which the water is drawn in a given locality and JIaY change materially 10 water from the same beds in different localities, even those that are adjacent, In many areas, ground waters are as good or better in quality than available surface water, and since they can often be used without treatment, may be preferred by prospective users. Bacteriological Quality Bacteriological quality of ground water in the AWR basins is not a limiting characteristic from the standpoint of municipal use. \Vhile there are exceptions, in general the bacteriological quality of water derived ' from properly located, designed and constructed wells is good. In those instances .vhere bacteriological quality is a problem, this can be solved by suitable .vater treatment methods. Poor bacteriological quality usually results from poor well location, faulty design or construction or improper maintenance. Failure to plug abandoned wells in the vicinity of active water supply wells and the use of the former as leaching cesspools is another reason for poor bacteriological quality of some underground water supplies. Physical and Chemical Quality Ini'ormation as to the quality of ground waters which can be developed in the Arkansas-White-Red River Basins is far from complete. In some areas, 5-3