Water

Water in three states: Liquid, solid (ice), and (invisible) vapor in air. Clouds are droplets of liquid, condensed from water vapor.
Water is a common chemical substance that is essential for the survival of all known forms of life.[1] 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. About 1,460 teratonnes (Tt) of water covers 71% of the Earth's surface, 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.[2] Some of the Earth's water is contained within man-made and natural objects near the Earth's surface such as water towers, animal and plant bodies, manufactured products, and food stores.
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%. 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, about 36 Tt per year. Over land, evaporation and transpiration contribute another 71 Tt per year to the precipitation of 107 Tt per year over land. Some water is trapped for varying periods in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land. Clean, fresh water is essential to human and other life. However, in many parts of the world - especially developing countries - it is in short supply. Water is a solvent for a wide variety of chemical substances.

Types of water


Liquid water in motion
Water can appear in three phases. Water takes many different forms on Earth: water vapor and clouds in the sky; seawater and rarely icebergs in the ocean; glaciers and rivers in the mountains; and aquifers in the ground.
Water can dissolve many different substances, giving it different tastes and odors. In fact, humans and other animals have developed senses to be able to evaluate the potability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer. Humans also tend to prefer cold water rather than lukewarm, as cold water is likely to contain less microbes. The taste advertised in spring water or mineral water derives from the minerals dissolved in it, as pure H2O is tasteless. As such, purity in spring and mineral water refers to purity from toxins, pollutants, and microbes.
Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: