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 crisis in the Democratic Republic of the Congo that they require only minimal investment to install and maintain. However, springs are often exploited without adequate protection and development. Another important source of water supply in rural areas are shallow wells, using hand and machine pumps. Other rural water supply sources include boreholes, small piped distribution systems and rainwater harvesting systems. Generally, charges for rural water systems do not cover operational costs. Furthermore, almost no water quality testing is conducted. Current investments in the rural water sector aim at the expansion of borehole drilling and small piped networks in large villages, which each serve between 2,000 and 5,000 people