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Fresh water (or freshwater) is any naturally occurring
water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all ...
except seawater and
brackish water Brackish water, also sometimes termed brack water, is water occurring in a natural environment having more salinity File:IAPSO Standard Seawater.jpg, upInternational Association for the Physical Sciences of the Oceans (IAPSO) standard seawater. ...
. Fresh water is generally characterized by having low
concentration In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they unde ...

concentration
s of dissolved salts and other total dissolved solids. Though the term specifically excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs. Fresh water may include water in
ice sheet
ice sheet
s,
ice cap upright=1.35, Vatnajökull, Iceland ">Iceland.html" ;"title="Vatnajökull, Iceland">Vatnajökull, Iceland In glaciology, an ice cap is a mass of ice that covers less than of land area (usually covering a highland area). Larger ice masses coveri ...
s,
glacier A glacier ( or ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. Glaciers slo ...
s, icebergs, bogs,
pond A pond is an area filled with water, either natural or artificial, that is smaller than a lake A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river A river is a natural flowing waterco ...
s,
lake A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a ri ...
s,
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Sm ...
s,
stream A stream is a body of water with surface water flowing within the stream bed, bed and Bank (geography), banks of a Channel (geography), channel. The flow of a stream is controlled by three inputs – surface water, subsurface water and ground ...
s, and even underground water called
groundwater Groundwater is the water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hyd ...
. Water is critical to the survival of all living organisms. Some organisms can thrive on salt water, but the great majority of higher plants and most
mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk ...
s need fresh water to live. Fresh water is not always
potable water
potable water
, that is, water safe to drink. Much of the earth's fresh water (on the surface and groundwater) is to a substantial degree unsuitable for human consumption without some treatment. Fresh water can easily become Water pollution, polluted by human activities or due to naturally occurring processes, such as erosion.


Definitions


Numerical definition

Fresh water can be defined as water with less than 500 parts per million (ppm) of dissolved salt (chemistry), salts. Other sources give higher upper salinity limits for fresh water, e.g. 1000 ppm or 3000 ppm.


Systems

File:Earth water distribution.svg, upright=1.3, Visualisation of the distribution (by volume) of water on Earth. Each tiny cube (such as the one representing biological water) corresponds to approximately 1400 cubic km of water, with a mass of approximately 1.4 trillion tonnes (235000 times that of the Great Pyramid of Giza or 8 times that of Lake Kariba, arguably the heaviest man-made object). The entire block comprises 1 million tiny cubes. Fresh water habitats are classified as either lake ecosystem, lentic systems, which are the stillwaters including
pond A pond is an area filled with water, either natural or artificial, that is smaller than a lake A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river A river is a natural flowing waterco ...
s, lakes, swamps and Bog, mires; lotic which are running-water systems; or
groundwater Groundwater is the water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hyd ...
s which flow in rocks and aquifers. There is, in addition, a zone which bridges between groundwater and lotic systems, which is the hyporheic zone, which underlies many larger rivers and can contain substantially more water than is seen in the open channel. It may also be in direct contact with the underlying underground water. The majority of fresh water on Earth is in
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s.


Sources

The source of almost all fresh water is Precipitation (meteorology), precipitation from the Earth's atmosphere, 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. However they can be as well found in glaciers, lakes, reservoirs. Also in areas such as ponds, rivers, streams, wetlands and even groundwater they can be found. In Industrialization, 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 some cases this acid rain results in pollution of lakes and rivers. In agricultural areas the lack of sewage and waste treatment has led to the quality of fresh water to become very toxic and create certain diseases or even birth defects. This has led to a reduction Of animals and a decrease of recreational activities in outside areas. 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.


Water distribution

Saline water in oceans, seas and saline
groundwater Groundwater is the water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hyd ...
make up about 97% of all the water on Earth. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in
glacier A glacier ( or ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. Glaciers slo ...
s, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in
lake A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a ri ...
s, swamps and
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Sm ...
s. Freshwater lakes contain about 87% of this fresh surface water, including 29% in the African Great Lakes, 22% in Lake Baikal in Russia, 21% in the North American Great Lakes, and 14% in other lakes. 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 (meteorology), 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 sheet
ice sheet
s. Many areas suffer from lack of distribution of fresh water, such as deserts.


Aquatic organisms

Water is a critical issue for the survival of all living organisms. Some can use salt water but many organisms including the great majority of higher plants and most
mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk ...
s must have access to fresh water to live. Some terrestrial mammals, especially desert rodents, appear to survive without drinking, but they do generate water through the metabolism of cereal seeds, and they also have mechanisms to conserve water to the maximum degree. Fresh water creates a Hypotonicity, hypotonic environment for aquatic organisms. This is problematic for some organisms with pervious skins or with gill membranes, whose cell membranes may burst if excess water is not excreted. Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney. Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, diadromous fish have the ability to Fish migration, migrate between fresh water and seawater, saline water bodies. During these migrations they undergo changes to adapt to the surroundings of the changed salinities; these processes are hormonally controlled. The eel (''Anguilla anguilla'') uses the hormone prolactin, while in salmon (''Salmo salar'') the hormone cortisol plays a key role during this process. 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. Freshwater molluscs include freshwater snails and freshwater bivalves. Freshwater crustaceans include freshwater crabs and crayfish. Unfortunately freshwater biodiversity faces many threats. The World Wide Fund for Nature's Living Planet Index noted an 83% decline in the populations of freshwater vertebrates between 1970 and 2014. These declines continue to outpace contemporaneous declines in marine or terrestrial systems. The causes of these declines are varied but are related to what Reid et al. call the "dirty dozen". The dirty dozen are: # A rapidly changing climate # Online wildlife trade and invasive species # Infectious disease # Toxic algae blooms # Hydropower damming and fragmenting of half the world's rivers # Emerging contaminants, such as hormones # Engineered nanomaterials # Microplastic pollution # Light and noise interference # Saltier coastal freshwaters due to sea level rise # Calcium concentrations falling below the needs of some freshwater organisms # The additive—and possibly synergistic—effects of these threats


Problems


Limited resource

Fresh water is a renewable and variable, but finite natural resource. Fresh water can only be replenished through the process of the water cycle, in which water from seas, lakes, forests, land, rivers, and reservoirs evaporates, forms clouds, and returns as precipitation. Locally, however, if more fresh water is consumed through human activities than is naturally restored, this may result in reduced fresh water availability from surface and underground sources and can cause serious damage to surrounding and associated environments. Fresh and unpolluted water accounts for 0.003% of total water available globally. However the downgrade of fresh water quality has been putting about 30% of amphibians and 50% of fish species that need fresh water at as possible risk of extinction The increase in the world population and the increase in per capita water use puts increasing strains on the finite resources availability of clean fresh water. The World Bank adds that the response by freshwater ecosystems to a changing climate can be described in terms of three interrelated components: water quality, water quantity or volume, and water timing. A change in one often leads to shifts in the others as well. Water pollution and subsequent eutrophication also reduces the availability of fresh water. Many areas of the world are already experiencing stress on water availability (or water scarcity). Due to the accelerated pace of population growth and an increase in the amount of water a single person uses, it is expected that this situation will continue to get worse. Areas on the planet with dry climates or hot weather such as deserts may not have access to as much freshwater as areas with a more cool or tropical climate. By the year 2050 almost half of the world's population will have very little access to freshwater. A shortage of water in the future would be detrimental to the human population as it would affect everything from sanitation, to overall health and the production of grain. Fresh water distribution has become a problem the past years and is now becoming a public health problem and starting many political arguments. Issues with distribution of freshwater can as well begin from activities conducted upstream from a river which will affect how people are communities living downstream will receive the water and in what condition it will be.


Minimum streamflow

An important concern for hydrological ecosystems is securing minimum streamflow, especially preserving and restoring Instream use, instream water allocations. Fresh water is an important natural resource necessary for the survival of all ecosystems. The use of water by humans for activities such as irrigation and industrial applications can have adverse impacts on down-stream ecosystems. Fresh water withdrawal is the quantity of water removed from available sources for use in any purpose, excluding evaporation losses. Water drawn off is not necessarily entirely consumed and some portion may be returned for further use downstream.


Water pollution

Water pollution, Pollution from human activity, including oil spills and also presents a problem for freshwater resources. The largest petroleum spill that has ever occurred in fresh water was caused by a Royal Dutch Shell tank ship in Magdalena, Argentina, on 15 January 1999, polluting the environment, drinkable water, plants and animals. Chemical contamination of fresh water can also seriously damage eco-systems. Of all the water that there is on Earth only 1% of it is fresh water. And from that 1% it all has to provide for us and they mostly come from the atmosphere, lakes, rivers, and underground areas. And due to industrial plants, agricultural farming, and many other operations this causes pollutants or chemicals to reach spots that do contain fresh water to be contaminated.


Human uses

Uses of water include agricultural, Industrial sector, industrial, household, recreational and Natural environment, environmental activities. Water used for agriculture is called "agricultural water" or farm water.


See also

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References


External links


The World Bank's work and publications on water resources



Fresh Water National Geographic
{{Authority control Fresh water, Aquatic ecology Hydrology Water supply