In ancient cities, covered channels or pipes were often used for removing human wastes from dwellings. Rome, for example, had a system of sewers for disposing of wastes and rainwater. Most ancient sewers fell into disrepair during the Middle Ages. Refuse and human wastes were commonly thrown into the streets. By the late 1700's, many large cities had sewers for removing storm water, but cesspools were usually used for sewage disposal. Both cesspools and privies were widely used in cities and towns.
Modern sewage disposal systems were introduced in the 19th century. Existing storm sewers were usually enlarged to carry both rainwater and wastes. In the late 19th century, either combined sewers or sanitary sewers were used for disposing of sewage and industrial wastes. The wastes were usually discharged into nearby bodies of water.
Municipal sewage treatment was introduced in the early 20th century, but many cities and industrial plants were slow to adopt it. As the population increased, some existing sewage plants became inadequate. In cities with combined sewers, heavy rains periodically overloaded otherwise adequate disposal facilities. By the 1970's, water pollution caused by the discharge of untreated or inadequately treated sewage had become a major problem. In the United States, legislation was passed in the 1970's to help control and prevent water pollution. The legislation set standards for the quality of treated sewage discharged into streams and lakes and established funding to assist in the improvement and construction of sewage treatment facilities. Additional legislation passed in the 198O's set standards for storm water discharges.