Properties of water equal to that of the hydrogen ion (), which gives a pH of 7 at 25 °C. Action of water on rock over long periods of time typically leads to weathering and water erosion, physical processes that convert solid rocks and minerals into soil and sediment, but under some conditions chemical reactions with water occur as well, resulting in metasomatism or mineral hydration, a type of chemical alteration of a rock which produces clay minerals. It also occurs when Portland cement hardens. Water ice can form clathrate compounds, known as clathrate hydrates, with a variety of small molecules that can
Water pollution in the United States which started to increase after the restriction to ocean dumping, helps reduce pollution particularly in areas where the surface water is not capable of assimilating elements such as nitrogen and phosphorus. The excessive amount of these chemical elements lead to pollution. With the widespread implementation of secondary treatment technology, water quality has greatly improved in many watersheds nationwide. However, many municipal plants are being challenged to confront some significant remaining problems: A growing body of water research during the late 1970s and 1980s indicated that stormwater runoff was a significant cause of water quality impairment in many parts of the