Editing Water (section)

==Water on Earth==


Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is hydrography. The study of the distribution and movement of groundwater is hydrogeology, of glaciers is glaciology, of inland waters is limnology and distribution of oceans is oceanography. Ecological processes with hydrology are in focus of ecohydrology.

The collective mass of water found on, under, and over the surface of a planet is called hydrosphere. Earth's approximate water volume (the total water supply of the world) is 1&nbsp;360&nbsp;000&nbsp;000&nbsp;km³ (326&nbsp;000&nbsp;000&nbsp;mi³). Of this volume:

* 1&nbsp;320&nbsp;000&nbsp;000&nbsp;km³ (316&nbsp;900&nbsp;000&nbsp;mi³ or 97.2%) is in the sea water|oceans.
* 25&nbsp;000&nbsp;000&nbsp;km³ (6&nbsp;000&nbsp;000&nbsp;mi³ or 1.8%) is in glaciers, ice caps and ice sheets.
* 13&nbsp;000&nbsp;000&nbsp;km³ (3,000,000 mi³ or 0.9%) is groundwater.
* 250&nbsp;000&nbsp;km³ (60,000 mi³ or 0.02%) is fresh water in lakes, inland seas, and rivers.
* 13&nbsp;000&nbsp;km³ (3,100 mi³ or 0.001%) is atmospheric water vapor at any given time.

Groundwater and fresh water are useful or potentially useful to humans as water resources.

Liquid water is found in '''bodies of water''', such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is sea water. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater in aquifers.

The most important geological processes caused by water are: Weathering, erosion, water sediment transport and sedimentation, mudflows, ice erosion and sedimentation by glacier.

===Water cycle===
Main|Water cycle

The water cycle (known scientifically as the '''hydrologic cycle''') refers to the continuous exchange of water within the hydrosphere, between the Earth atmosphere|atmosphere, soil water, surface water, groundwater, and plants.

Water moves perpetually through each of these regions in the ''water cycle'' consisting of following transfer processes:
*evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into air.
*precipitation, from water vapor condensing from the air and falling to earth or ocean.
*runoff from the land usually reaching the sea.
Most water vapor over the oceans returns to the oceans, but winds carry water vapor over land at the same rate as runoff into the sea, about 36 Tonne#Multiples|Tt per year. Over land, evaporation and transpiration contribute another 71 Tt per year. Precipitation, at a rate of 107 Tt per year over land, has several forms: most commonly rain, snow, and hail, with some contribution from fog and dew. Condensed water in the air may also refract sunlight to produce rainbows.

Water runoff often collects over watersheds flowing into rivers. A mathematical model used to simulate river or stream flow and calculate water quality parameters is hydrological transport model. Some of water is diverted to irrigation for agriculture. Rivers and seas offer opportunity for travel and commerce. Through erosion, runoff shapes the environment creating river valleys and river delta|deltas which provide rich soil and level ground for the establishment of population centers. A flood occurs when an area of land, usually low-lying, is covered with water. It is when a river overflows its banks or flood from the sea. A drought is an extended period of months or years when a region notes a deficiency in its water supply. This occurs when a region receives consistently below average precipitation.

===Tides===

'''Tides''' are the cyclic rising and falling of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuary|estuarine water bodies and produce oscillating currents known as tidal streams. 
The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the Coriolis effect|effects of Earth rotation and the local bathymetry. The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides.