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
Drinking water supply and sanitation in the United States water quality that are of some concern in the United States, including Cryptosporidium, disinfection by-products, lead, perchlorates and pharmaceutical substances. However, in almost all cases drinking water quality is in conformity with the norms of the Safe Drinking Water Act, which requires EPA to set Maximum Contaminant Levels for pollutants. In addition, the EPA's Consumer Confidence Rule of 1998 requires most public water suppliers to provide consumer confidence reports, also known as annual water quality reports, to their customers. Each year by July 1 anyone connected to a public water system should receive in the mail an annual water quality