Water treatment-or the purification and sanitation of water-varies as to the source and kinds of water. Municipal waters, for example, consist of surface water and ground water, and their treatment is to be distinguished from that of industrial water supplies. Municipal water supplies are treated by public or private water utilities to make the water potable (safe to drink) and palatable (aesthetically pleasing) and to insure an adequate supply of water to meet the needs of the community at a reasonable cost.
Except in exceedingly rare instances, the entire supply is treated to drinking water quality for three reasons: it is generally not feasible to supply water of more than one quality; it is difficult to control public access to water not treated to drinking water quality; and a substantial amount of treatment may be required even if the water is not intended for human consumption.
There are a number of other processes that may be employed to treat water, depending on the quality of the source water and the desired quality of the treated water. Processes that may be used to treat either surface water or groundwater include:
1)lime softening, which involves the addition of lime during rapid mixing to precipitate calcium and magnesium ions;
2)stabilization, to prevent corrosion and scale formation, usually by adjusting the pH or alkalinity of the water or by adding scale inhibitors;
3)activated carbon adsorption, to remove taste- and odor-causing chemicals or synthetic organic contaminants; and
4)fluoridation, to increase the concentration of fluoride to the optimum level for the prevention of dental cavities.