question: How does salt water from the oceans turn into fresh water in rivers and lakes?
comment: When water evaporates from the sea it leaves behind the salt, so when the clouds rain it onto the mountains it's fresh with no salt in it
passages: 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 some cases this acid rain results in pollution of lakes and rivers.
   Section::::Estuarine and coastal ecosystem services.:Provisioning Services.:Fresh water.
  
  Water bodies that are not highly concentrated in salts are referred to as 'fresh water' bodies. Fresh water may run through lakes, rivers and streams, to name a few; but it is most prominently found in the frozen state or as soil moisture or buried deep underground. Fresh water is not only important for the survival of humans, but also for the survival of all the existing species of animals, plants.
  
  Section::::Estuarine and coastal ecosystem services.:Provisioning Services.:Raw materials.
   Salt is expensive to remove from water, and salt content is an important factor in water use (such as potability). Increases in salinity have been observed in lakes and rivers in the United States, due to common road salt and other salt de-icers in runoff.
   The remainder of the Earth's water constitutes the planet's "fresh water" resource. Typically, fresh water is defined as water with a salinity of "less than 1 percent that of the oceans" - i.e. below around 0.35‰. Water with a salinity between this level and 1‰ is typically referred to as "marginal water" because it is marginal for many uses by humans and animals. The ratio of salt water to fresh water on Earth is around 50 to 1.
   The degree of salinity in oceans is a driver of the world's ocean circulation, where density changes due to both salinity changes and temperature changes at the surface of the ocean produce changes in buoyancy, which cause the sinking and rising of water masses. Changes in the salinity of the oceans are thought to contribute to global changes in carbon dioxide as more saline waters are less soluble to carbon dioxide. In addition, during glacial periods, the hydrography is such that a possible cause of reduced circulation is the production of stratified oceans. In such cases, it is more difficult to subduct water through the thermohaline circulation.
   Section::::Forcing mechanisms.
  
  In coastal areas the groundwater and seawater flows are driven by a variety of factors. Both types of water can circulate in marine sediments due to tidal pumping, waves, bottom currents or density driven transport processes. Meteoric freshwaters can discharge along confined and unconfined aquifers into the sea or the oppositional process of seawater intruding into groundwater charged aquifers can take place. The flow of both fresh and sea water is primarily controlled by the hydraulic gradients between land and sea and differences in the densities between both waters and the permeabilities of the sediments.
   Saline water in oceans, seas and saline groundwater make up about 97% of all the water on Earth. 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. 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 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 areas suffer from lack of distribution of fresh water, such as deserts.
   BULLET::::- temperature – is affected by geographical latitude, ocean currents, weather, the discharge of rivers, and by the presence of hydrothermal vents or cold seeps
  
  BULLET::::- sunlight – photosynthetic processes depend on how deep and turbid the water is
  
  BULLET::::- nutrients – are transported by ocean currents to different marine habitats from land runoff, or by upwellings from the deep sea, or they sink through the sea as marine snow
  
  BULLET::::- salinity – varies, particularly in estuaries or near river deltas, or by hydrothermal vents
   If the surface water source is also subject to substantial evaporation, a groundwater source may become saline. This situation can occur naturally under endorheic bodies of water, or artificially under irrigated farmland. In coastal areas, human use of a groundwater source may cause the direction of seepage to ocean to reverse which can also cause soil salinization. Humans can also cause groundwater to be "lost" (i.e. become unusable) through pollution. Humans can increase the input to a groundwater source by building reservoirs or detention ponds.
  
  Section::::Sources of fresh water.:Frozen water.
   Fresh water habitats are classified as either lentic systems, which are the stillwaters including ponds, lakes, swamps and mires; lotic which are running-water systems; or groundwaters 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 ice caps.
  
  Section::::Sources.
   Atmospheric circulation moves water vapor around the globe; cloud particles collide, grow, and fall out of the upper atmospheric layers as precipitation. Some precipitation falls as snow or hail, sleet, and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Most water falls back into the oceans or onto land as rain, where the water flows over the ground as surface runoff. A portion of runoff enters rivers in valleys in the landscape, with streamflow moving water towards the oceans. Runoff and water emerging from the ground (groundwater) may be stored as freshwater in lakes. Not all runoff flows into rivers; much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and replenishes aquifers, which can store freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into surface-water bodies (and the ocean) as groundwater discharge. Some groundwater finds openings in the land surface and comes out as freshwater springs. In river valleys and floodplains, there is often continuous water exchange between surface water and ground water in the hyporheic zone. Over time, the water returns to the ocean, to continue the water cycle.
   Water used for agriculture is called "agricultural water" or "farm water." Changing landscape for the use of agriculture has a great effect on the flow of fresh water. Changes in landscape by the removal of trees and soils changes the flow of fresh water in the local environment and also affects the cycle of fresh water. As a result, more fresh water is stored in the soil which benefits agriculture. However, since agriculture is the human activity that consumes the most fresh water, this can put a severe strain on local freshwater resources resulting in the destruction of local ecosystems.
   For practical reasons salinity is usually related to the sum of masses of a subset of these dissolved chemical constituents (so-called "solution salinity"), rather than to the unknown mass of salts that gave rise to this composition (an exception is when artificial seawater is created). For many purposes this sum can be limited to a set of eight major ions in natural waters, although for seawater at highest precision an additional seven minor ions are also included. The major ions dominate the inorganic composition of most (but by no means all) natural waters. Exceptions include some pit lakes and waters from some hydrothermal springs.
   Section::::On Earth.:Water cycle.
  
  The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.
  
  Water moves perpetually through each of these regions in the "water cycle" consisting of the following transfer processes:
  
  BULLET::::- evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into the air.
  
  BULLET::::- precipitation, from water vapor condensing from the air and falling to the earth or ocean.
  
  BULLET::::- runoff from the land usually reaching the sea.
   While the water cycle is itself a biogeochemical cycle, flow of water over and beneath the Earth is a key component of the cycling of other biogeochemicals. Runoff is responsible for almost all of the transport of eroded sediment and phosphorus from land to waterbodies. The salinity of the oceans is derived from erosion and transport of dissolved salts from the land. Cultural eutrophication of lakes is primarily due to phosphorus, applied in excess to agricultural fields in fertilizers, and then transported overland and down rivers. Both runoff and groundwater flow play significant roles in transporting nitrogen from the land to waterbodies. The dead zone at the outlet of the Mississippi River is a consequence of nitrates from fertilizer being carried off agricultural fields and funnelled down the river system to the Gulf of Mexico. Runoff also plays a part in the carbon cycle, again through the transport of eroded rock and soil.
   Most are naturally occurring geographical features, but some are artificial. There are types that can be either. For example, most reservoirs are created by engineering dams, but some natural lakes are used as reservoirs. Similarly, most harbors are naturally occurring bays, but some harbors have been created through construction.
  
  Bodies of water that are navigable are known as waterways. Some bodies of water collect and move water, such as rivers and streams, and others primarily hold water, such as lakes and oceans.
   Section::::Global change.
   BULLET::::- Without the inflow from the Atlantic, the Mediterranean would evaporate much more water than it receives, and would evaporate down to two large lakes, one on the Balearic Abyssal Plain, the other further east.
  
  BULLET::::- The east lake would receive most of the incoming river water, and may have overflowed into the west lake.
  
  BULLET::::- All or some of this seabed may have had a human population, where it was watered from the incoming rivers.
  
  BULLET::::- There is a long deep submerged valley running from the Mediterranean out into the Atlantic.
   Section::::Sources of fresh water.:Under river flow.
   Section::::Classification based on water circulation.:Partially mixed.
  
  As tidal forcing increases, river output becomes less than the marine input. Here, current induced turbulence causes mixing of the whole water column such that salinity varies more longitudinally rather than vertically, leading to a moderately stratified condition. Examples include the Chesapeake Bay and Narragansett Bay.
  
  Section::::Classification based on water circulation.:Well-mixed.
   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.
   Section::::Ecology of fresh water.
   The planet's fresh water is also very unevenly distributed. Although in warm periods such as the Mesozoic and Paleogene when there were no glaciers anywhere on the planet all fresh water was found in rivers and streams, today most fresh water exists in the form of ice, snow, groundwater and soil moisture, with only 0.3% in liquid form on the surface. Of the liquid surface fresh water, 87% is contained in lakes, 11% in swamps, and only 2% in rivers. Small quantities of water also exist in the atmosphere and in living beings. Of these sources, only river water is generally valuable.
   Over millions of years, the Colorado River has flowed into the Imperial Valley and deposited soil (creating fertile farmland), building up the terrain and constantly changing the course of the river. For thousands of years, the river has alternately flowed into and out of the valley, alternately creating a freshwater lake, an increasingly saline lake, and a dry desert basin, depending on river flows and the balance between inflow and evaporative loss. The cycle of filling has been about every 400–500 years and has repeated many times. The latest natural cycle occurred around 1600–1700 as remembered by Native Americans who talked with the first European settlers. Fish traps still exist at many locations, and the Native Americans evidently moved the traps depending upon the cycle.
   BULLET::::- A salt lake, which also known as a "brine lake", is an inland body of water situated in an arid or semiarid region, having no outlet to the sea, and containing a high concentration of dissolved salts (principally sodium chloride). Examples include the Great Salt Lake in Utah, and the Dead Sea in the Near East.
  