The threat to public health became apparent. In densely populated areas, local conditions soon became intolerable because the cesspools were seldom emptied and frequently overflowed. Toilets (water closets) were installed in houses in the early 19th century, but they were usually connected to cesspools, not to sewers. Privy vaults and cesspools were used, but most wastes were simply dumped into gutters to be flushed through the drains by floods. There was little progress in urban drainage or sewerage during the Middle Ages. Built of stone and on a grand scale, the Cloaca Maxima is one of the oldest existing monuments of Roman engineering. It included many surface conduits that were connected to a large vaulted channel called the Cloaca Maxima (“Great Sewer”), which carried drainage water to the Tiber River. A notable example is the drainage system of ancient Rome. Many ancient cities had drainage systems, but they were primarily intended to carry rainwater away from roofs and pavements. Historical background Direct discharge of sewage Water pollution, therefore, is caused primarily by the drainage of contaminated wastewater into surface water or groundwater, and wastewater treatment is a major element of water pollution control. Although water quality is affected by natural conditions, the word pollution usually implies human activity as the source of contamination. In broad terms, water is said to be polluted when it contains enough impurities to make it unfit for a particular use, such as drinking, swimming, or fishing. Since pure water is not found in nature (i.e., outside chemical laboratories), any distinction between clean water and polluted water depends on the type and concentration of impurities found in the water as well as on its intended use. Wastewater treatment, also called sewage treatment, the removal of impurities from wastewater, or sewage, before it reaches aquifers or natural bodies of water such as rivers, lakes, estuaries, and oceans.
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