Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids. The term specifically excludes seawater and brackish water although it does include mineral rich waters such as chalybeate springs. The term "sweet water" has been used to describe fresh water in contrast to salt water.
The source of almost all fresh water is precipitation from the atmosphere, in the form of mist, rain and snow. Fresh water falling as mist, rain or snow contains materials dissolved from the atmosphere and material from the sea and land over which the rain bearing clouds have traveled. In industrialized areas rain is typically acidic because of dissolved oxides of sulfur and nitrogen formed from burning of fossil fuels in cars, factories, trains and aircraft and from the atmospheric emissions of industry. In extreme cases this acid rain results in pollution of lakes and rivers in parts of Scandinavia, Scotland, Wales and the United States.
In coastal areas fresh water may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds. This can give rise to elevated concentrations of sodium, chloride, magnesium and sulfate as well as many other compounds in smaller concentrations.
In desert areas, or areas with impoverished or dusty soils, rain-bearing winds can pick up sand and dust and this can be deposited elsewhere in precipitation and causing the freshwater flow to be measurably contaminated both by insoluble solids but also by the soluble components of those soils. Significant quantities of iron may be transported in this way including the well-documented transfer of iron-rich rainfall falling in Brazil derived from sand-storms in the Sahara in north Africa.
{| style="margin-left:auto; margin-right:auto;" |- ! style="background:#B8E0F6" colspan="4" | Water salinity based on dissolved salts in parts per thousand (‰) |- ! style="background:#87CEFA" | Fresh water ! style="background:#87CEFA" | Brackish water ! style="background:#87CEFA" | Saline water ! style="background:#87CEFA" | Brine |- ! style="background:#00BFFF" | < 0.5 ! style="background:#00BFFF" | 0.5 – 30 ! style="background:#00BFFF" | 30 – 50 ! style="background:#00BFFF" | > 50 |}
Other sources give higher upper salinity limits for fresh water, e.g. 1000 ppm or 3000 ppm.
Out of all the water on Earth, only 2.75 percent is fresh water, including 2.05 percent frozen in glaciers, 0.68 percent as groundwater and 0.011 percent of it as surface water in lakes and rivers. Freshwater lakes, most notably Lake Baikal in Russia and the Great Lakes in North America, contain seven-eighths of this fresh surface water. Swamps have most of the balance with only a small amount in rivers, most notably the Amazon River. The atmosphere contains 0.04% water. In areas with no fresh water on the ground surface, fresh water derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers. Most of the world's fresh water is frozen in ice sheets.
Many sea birds have special glands at the base of the bill through which excess salt is excreted. Similarly the Marine Iguanas on the Galápagos Islands excrete excess salt through a nasal gland and they sneeze out a very salty excretion.
Pollution from human activity, including oil spills, also presents a problem for freshwater resources. The largest oil spill that has ever occurred in fresh water was caused by a Shell tank ship in Magdalena, Argentina, on January 15, 1999, polluting the environment, drinkable water, plants and animals.
Fresh and unpolluted water accounts for 0.003% of total water available globally.
"If global warming continues to melt glaciers in the polar regions, as expected, the supply of fresh water may actually decrease. First, fresh water from the melting glaciers will mingle with salt water in the oceans and become too salty to drink. Second, the increased ocean volume will cause sea levels to rise, contaminating freshwater sources along coastal regions with seawater”.Water pollution and subsequent eutrophication also reduces the availability of fresh water.
Category:Aquatic ecology Category:Liquid water Category:Hydrology
ar:ماء عذب ca:Aigua dolça cs:Sladká voda da:Ferskvand de:Süßwasser et:Magevesi es:Agua dulce eo:Nesala akvo eu:Ur geza fa:آب شیرین fr:Eau douce fy:Swietwetter gl:Auga doce ko:민물 hr:Slatka voda id:Air tawar is:Ferskvatn it:Acqua dolce he:מים מתוקים kk:Тұщы көл sw:Maji matamu lv:Saldūdens lb:Séisswaasser hu:Édesvíz mk:Питка вода ms:Air tawar nl:Zoet water ja:淡水 no:Ferskvann nn:Ferskvatn nds:Söötwater pl:Woda słodka pt:Água doce ru:Пресная вода sah:Ньулуун уу sco:Fresh watter simple:Fresh water fi:Makea vesi sv:Sötvatten ta:நன்னீர் th:น้ำจืด tr:Tatlı su uk:Прісні води vi:Nước ngọt war:Tab-áng zh-yue:淡水 zh:淡水This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
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