Abstract

An essentially constant supply of water is available for utilization by all living creatures; however, it is necessary to manage the water resources of a region in such a way that the available water meets all legitimate needs.

Use dictates the quality required. Potable water must be bacteriologically safe, and toxic substances must be present at levels that are accepted as safe. In addition, the water must be aesthetically acceptable. Water that is suitable for drinking may be inadequate for many industrial processes. On the other hand, many industrial processes can use water that is not pure enough to drink.

Formerly, water was accepted by a second user for reuse while it was still under control of the first user. Today, the used water is treated in such a manner that is can be used again before ultimate disposal. Furthermore, a distinction can be made between direct reuse, where the water is reclaimed without dilution or natural purification, and indirect use, where treated used water is returned to the environment for subsequent utilization as a raw water supply.

Water can seldom be reused directly. The treatment required depends on the intended second use. Disposal costs of the wastewater must be included in any economic analysis, and additional treatment for reuse may be justified when this expense is included. Costs of reclamation depend on the location, water scarcity, availability of public water supplies, and the intended reuse. Various treatments are discussed in the article.

Pure water is expensive, and high quality sources are becoming more scarce. It is frequently necessary to accept lower quality water and subject it to costly treatment. Used water as a source of raw water supply has long been permitted by public health authorities in water-poor areas. However, in regions with an ample supply of fresh drinking water, there is resistance to the inclusion of reused water.