Energy & Green Tech

Simple, solar-powered water desalination

A completely passive solar-powered desalination system developed by researchers at MIT and in China could provide more than 1.5 gallons of fresh drinking water per hour for every square meter of solar collecting area. Such ...


Device mimics the mangrove's water-purifying power

The mangrove tree survives in its subtropical habitat by efficiently converting the salty water of its environment into fresh water—an engineering feat that has long baffled scientists.

Energy & Green Tech

Could water solve the renewable energy storage challenge?

Seasonal pumped hydropower storage (SPHS), an already established yet infrequently used technology, could be an affordable and sustainable solution to store energy and water on an annual scale, according to new IIASA research ...

Energy & Green Tech

Smart water heating could help in South Africa's energy crisis

South Africa's energy crisis has many dimensions, from political and economic to technical and environmental. Recently, the country's power utility, Eskom, has been generating only about 60% of its capacity and has had to ...

page 1 from 1


Water is a ubiquitous chemical substance, composed of hydrogen and oxygen, that is essential for the survival of many known forms of life. In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71% of the Earth's surface. On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation. Saltwater oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and ponds 0.6%. A very small amount of the Earth's water is contained within biological bodies and manufactured products. Other water is trapped in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land.

Water moves continually through a cycle of evaporation or transpiration (evapotranspiration), precipitation, and runoff, usually reaching the sea. Winds carry water vapor over land at the same rate as runoff into the sea. Over land, evaporation and transpiration contribute to the precipitation over land.

Clean, fresh drinking water is essential to human and other lifeforms. Access to safe drinking water has improved steadily and substantially over the last decades in almost every part of the world. There is a clear correlation between access to safe water and GDP per capita. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70 percent of freshwater is consumed by agriculture.

This text uses material from Wikipedia, licensed under CC BY-SA