In addition to water withdrawals, public-supply deliveries, and consumptive use, the term "water use" also includes wastewater releases and return flow. Because quality as well as quantity considerations are increasingly important in water management, more information is needed concerning the location of wastewater-treatment facilities and the quantities of treated wastewater released from the facilities and returned to the hydrologic system.
The wastewater treatment category includes information on facilities engaged primarily in the collection, treatment, and disposal of wastewater conveyed through a sewer system. Return of treated water generally is to surface waters. Treatment facilities are separated into two categories in this report: publicly owned (municipal) treatment works and "other". Publicly-owned treatment works are publicly owned or receive some form of public funding, and receive and treat wastewater from various users such as domestic, commercial, and industrial. Other wastewater facilities are privately owned and include commercial and industrial facilities that treat their own wastewater. Information on the quantities of water treated and released from publicly owned treatment facilities and returned directly to the hydrologic system, or released for beneficial reuse (reclaimed wastewater), are given in this report, along with the number of public and other wastewater-treatment facilities.
The release information usually is obtained from wastewater-treatment facility operators, utility departments, or from discharge permit files maintained by State or Federal agencies. Return flows to surface water usually are regulated by State or Federal agencies. The number of wastewater-treatment facilities typically is available from permit files at State or Federal agencies. The reliability of the data varies by State depending on available information.
About 19,600 public-treatment facilities released about 35,300 Mgal/d of treated wastewater nationwide during 1990. (See table 29 - hydrologic regions, table 30 - States.) Nationally, an average of from 1 million to 2 million gallons of treated wastewater per public-treatment facility was returned daily to streams or other surface-water bodies. In addition, 928 Mgal/d of treated wastewater was reclaimed for beneficial uses such as irrigation of golf courses and public parks. The largest return flows occurred in hydrologic regions (figure 31 (GIF file) (or as a PostScript file (620Kb)) and States (figure 32 (GIF file) or as a PostScript file (508Kb)) that have large populations and large public-supply withdrawals. California and New York, which have large public-supply withdrawals, reported the largest releases of treated wastewater. California, Arizona, and Florida reported large uses of reclaimed wastewater.