Europe. The Metropolitan Commission of Sewers was formed at the same time, water filtration was adopted throughout the country, and new water intakes on the Thames were established above Teddington Lock. Automatic pressure filters, where the water is forced under pressure through the filtration system, were innovated in 1899 in England. Limited drinking water standards were first implemented in the US in 1914, but it would not be until the 1940s that federal drinking water standards were widely applied. In 1972, the Clean Water Act passed through Congress and became law, requiring industrial plants to proactively improve their waste procedures in order to limit the effect of contaminants on freshwater sources. In 1974, the Safe Drinking Water Act was adopted by all 50 U.S. states for the regulation of public water systems within their jurisdictions. Softening and ion exchange By the early 1900s, water treatment experimentation had turned from the prevention of waterborne diseases to the creation of softer, less-mineralized water. Water softeners, which use sodium ions to replace water-hardening minerals in water, were first introduced into the water treatment market in 1903. The theory of ion exchange involves replacing undesirable or potentially harmful ions with more desirable or harmless ones. This is implemented in domestic water treatment system as water softeners. These not only remove calcium ions, but also lead and other heavy metals from water. See also Hot tub History of the Spa History of water supply and sanitation References Water filters Water treatment