Standards for water quality

The quality which is necessary depends on the use to which the water will be put. Because uses vary, so also must quality standards. Maintaining any level of quality presents a problem of cost and depends on variations in natural water characteristics, in time and space, and variations in volume and types of wastes. For quality standards appropriate to a given water body, hydrologic network data can provide duration curves of flow, concentrations of dissolved oxygen, dissolved solids, including nutrients (nitrates and phosphates), turbidity, temperature, and other significant chemical, physical, and biological parameters. Standards can then be expressed as occurrences in percentage of time or with respect to flow.