Fresh water

Fresh water (or freshwater) is any naturally occurring water except seawater and brackish water. Though the term specifically excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs.

Brackish water is water having more salinity than freshwater, but not as much as seawater.

Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater.

An iceberg or ice mountain is a large piece of freshwater ice that has broken off a glacier or an ice shelf and is floating freely in open water.

Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater. Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.

A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river.

Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater. Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.

Glacial ice is the largest reservoir of fresh water on Earth.

Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater. Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.

The majority of lakes on Earth are freshwater, and most lie in the Northern Hemisphere at higher latitudes.

Though the term specifically excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs. 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 migrate between fresh water and saline water bodies.

Seawater is denser than both fresh water and pure water (density 1.0 kg/L at 4 C) because the dissolved salts increase the mass by a larger proportion than the volume.

Fresh water habitats are classified as either lentic systems, which are the still-waters including ponds, lakes, swamps and mires ; lotic which are running-water systems; or groundwaters which flow in rocks and aquifers. Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.

The water of a swamp may be fresh water, brackish water or seawater.

The source of almost all fresh water is precipitation from the atmosphere, in the form of mist, rain and snow.

Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth.

Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater. Fresh water habitats are classified as either lentic systems, which are the still-waters including ponds, lakes, swamps and mires ; lotic which are running-water systems; or groundwaters which flow in rocks and aquifers. Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.

Groundwater makes up about twenty percent of the world's fresh water supply, which is about 0.61% of the entire world's water, including oceans and permanent ice.

Fresh water is not the same as potable water (or drinking water).

Approximately 97.2% of it is saline, just 2.8% fresh.

The source of almost all fresh water is precipitation from the atmosphere, in the form of mist, rain and snow.

Precipitation is a major component of the water cycle, and is responsible for depositing the fresh water on the planet.

Fresh water habitats are classified as either lentic systems, which are the still-waters including ponds, lakes, swamps and mires ; lotic which are running-water systems; or groundwaters which flow in rocks and aquifers.

Groundwater can be found at nearly every point in the Earth's shallow subsurface to some degree, although aquifers do not necessarily contain fresh water.

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.

Lake Baikal is the largest freshwater lake by volume in the world, containing 22–23% of the world's fresh surface water.

Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.

The remainder (about 0.65% of the whole) form underground reservoirs or various stages of the water cycle, containing the freshwater encountered and used by most terrestrial life: vapor in the air, the clouds it slowly forms, the rain falling from them, and the lakes and rivers spontaneously formed as its waters flow again and again to the sea.

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.

They include Lake Victoria, the third-largest fresh water lake in the world by area, and Lake Tanganyika, the world's second-largest freshwater lake by volume and depth.

Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney.

Freshwater fish are those that spend some or all of their lives in fresh water, such as rivers and lakes, with a salinity of less than 0.05%.

Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney.

In freshwater environments, the concentration of solutes is hypotonic, higher inside than outside the cell.

The eel (Anguilla anguilla) uses the hormone prolactin, while in salmon (Salmo salar) the hormone cortisol plays a key role during this process.

Typically, salmon are anadromous: they hatch in fresh water, migrate to the ocean, then return to fresh water to reproduce.

Freshwater molluscs include freshwater snails and freshwater bivalves.

Freshwater snails are gastropod mollusks which live in freshwater.

Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids.

Fresh water: TDS = 500 ppm

This is problematic for some organisms with pervious skins or with gill membranes, whose cell membranes may burst if excess water is not excreted.

In fresh water, the dissolved oxygen content is approximately 8 cm 3 /L compared to that of air which is 210 cm 3 /L. Water is 777 times more dense than air and is 100 times more viscous.

Out of all the water on Earth, saline water in oceans, seas and saline groundwater make up about 97% of it. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers, ice and snow, 0.5–0.75% as fresh groundwater and soil moisture, and less than 0.01% of it as surface water in lakes, swamps and rivers.

About 97.5% of the water is saline; the remaining 2.5% is fresh water.

Freshwater crustaceans include freshwater crabs and crayfish.

Some species are found in brooks and streams where there is running fresh water, while others thrive in swamps, ditches, and paddy fields.

Freshwater molluscs include freshwater snails and freshwater bivalves.

Freshwater molluscs are those members of the Phylum Mollusca which live in freshwater habitats, both lotic (flowing water) such as rivers, streams, canals, springs, and cave streams (stygobite species) and lentic (still water) such as lakes, ponds (including temporary or vernal ponds), and ditches.

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 migrate between fresh water and saline water bodies.

Fish species diversity is roughly divided equally between marine (oceanic) and freshwater ecosystems.