Fresh water: Difference between revisions - Wikipedia

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'''Fresh water''' or '''freshwater''' is any naturally occurring liquid or frozen [[water]] containing low [[concentration]]s of dissolved [[salt (chemistry)|salts]] and other [[total dissolved solids]]. Although the term specifically excludes [[seawater]] and [[brackish water]], it does include non-salty [[mineral water|mineral-rich water]]s such as [[chalybeate]] springs. Fresh water may encompass [[frozen water|frozen]] and [[meltwater]] in [[ice sheet]]s, [[ice cap]]s, [[glacier]]s, [[snowfield]]s and [[iceberg]]s, natural [[precipitation]]s such as [[rain]]fall, [[snowfall]], [[hail]]/[[ice pellets|sleet]] and [[graupel]], and [[surface runoff]]s that form inland [[bodies of water]] such as [[wetland]]s, [[pond]]s, [[lake]]s, [[river]]s, [[stream]]s, as well as [[groundwater]] contained in [[aquifer]]s, [[subterranea (geography)|subterranean]] [[subterranean river|river]]s and [[underground lake|lake]]s. Fresh water is the [[Water resources|water resource]] that is of the most and immediate use to humans.

Water is critical to the survival of all living [[organism]]s. Many organisms can thrive on salt water, but the great majority of [[~~higher~~vascular plant]]s and most [[insect]]s, [[amphibian]]s, [[reptile]]s, [[mammal]]s and [[bird]]s need fresh water to survive.

Fresh water is not always [[drinking water|potable water]], that is, water safe to drink by [[human]]s. 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. Fresh water makes up less than 3% of the world's water resources, and just 1% of that is readily available. Just 3% of it is extracted for human consumption. Agriculture uses roughly two thirds of all fresh water ~~abstracted~~extracted from the environment.<ref name=":68">{{Cite web |title=Wastewater resource recovery can fix water insecurity and cut carbon emissions |url=https://www.eib.org/en/essays/wastewater-resource-recovery |access-date=29 August 2022 |website=European Investment Bank |language=en |archive-date=29 August 2022 |archive-url=https://web.archive.org/web/20220829150040/https://www.eib.org/en/essays/wastewater-resource-recovery |url-status=live }}</ref><ref>{{Cite web |date=26 January 2010 |title=Competing for Clean Water Has Led to a Crisis |url=https://www.nationalgeographic.com/environment/article/freshwater-crisis |access-date=29 August 2022 |website=Environment |language=en |archive-date=19 February 2021 |archive-url=https://web.archive.org/web/20210219192438/https://www.nationalgeographic.com/environment/article/freshwater-crisis |url-status=dead }}</ref><ref>{{Cite web |title=Freshwater Resources {{!}} National Geographic Society |url=https://education.nationalgeographic.org/resource/freshwater-resources/ |access-date=29 August 2022 |website=education.nationalgeographic.org |archive-date=26 May 2022 |archive-url=https://web.archive.org/web/20220526195118/https://education.nationalgeographic.org/resource/freshwater-resources |url-status=live }}</ref>

Fresh water is a renewable and variable, but finite [[natural resource]]. Fresh water is replenished through the process of the natural [[water cycle]], in which water from seas, lakes, forests, land, rivers and [[reservoirs]] evaporates, forms [[cloud]]s, and returns inland as precipitation.<ref>{{Cite web|title=The Fundamentals of the Water Cycle|url=https://www.usgs.gov/special-topic/water-science-school/science/fundamentals-water-cycle?qt-science_center_objects=0#qt-science_center_objects|access-date=17 September 2021|website=www.usgs.gov|archive-date=27 November 2019|archive-url=https://web.archive.org/web/20191127053410/https://www.usgs.gov/special-topic/water-science-school/science/fundamentals-water-cycle?qt-science_center_objects=0#qt-science_center_objects|url-status=dead}}</ref> Locally, however, if more fresh water is consumed through human activities than is naturally restored, this may result in reduced fresh water availability (or [[water scarcity]]) from surface and underground sources and can cause serious damage to surrounding and associated environments. [[Water pollution]] also reduces the availability of fresh water. Where available water resources are scarce, humans have developed technologies like [[desalination]] and [[wastewater recycling]] to stretch the available supply further. However, given the high cost (both capital and running costs) and - especially for desalination - energy requirements, those remain mostly niche applications. A non-sustainable alternative is using so-called "[[fossil water]]" from underground [[aquifers]]. As some of those aquifers formed hundreds of thousands or even millions of years ago when local climates were wetter (e.g. from one of the [[Green Sahara]] periods) and are not appreciably replenished under current climatic conditions - at least compared to drawdown, these aquifers form essentially non-renewable resources comparable to peat or lignite, which are also continuously formed in the current era but orders of magnitude slower than they are mined.

==Definitions==

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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]].~~{{citation needed|date=June 2021}}~~<ref>{{Cite journal |last1=Rizzolo |first1=Joana A. |last2=Barbosa |first2=Cybelli G. G. |last3=Borillo |first3=Guilherme C. |last4=Godoi |first4=Ana F. L. |last5=Souza |first5=Rodrigo A. F. |last6=Andreoli |first6=Rita V. |last7=Manzi |first7=Antônio O. |last8=Sá |first8=Marta O. |last9=Alves |first9=Eliane G. |last10=Pöhlker |first10=Christopher |last11=Angelis |first11=Isabella H. |last12=Ditas |first12=Florian |last13=Saturno |first13=Jorge |last14=Moran-Zuloaga |first14=Daniel |last15=Rizzo |first15=Luciana V. |date=22 February 2017 |title=Soluble iron nutrients in Saharan dust over the central Amazon rainforest |url=https://www.researchgate.net/publication/314247273 |journal=Atmospheric Chemistry and Physics |volume=17 |issue=4 |pages=2673–2687 |doi=10.5194/acp-17-2673-2017 |bibcode=2017ACP....17.2673R |via=ResearchGate|hdl=10536/DRO/DU:30091978 |hdl-access=free |doi-access=free }}</ref>

In Africa, it was revealed that groundwater controls are complex and do not correspond directly to a single factor. Groundwater showed greater resilience to climate change than expected, and areas with an increasing threshold between 0.34 and 0.39 aridity index exhibited significant sensitivity to climate change. Land-use could affect infiltration and runoff processes. The years of most recharge coincided with the most precipitation anomalies, such as during [[El Niño]] and [[La Niña]] events. Three precipitation-recharge sensitivities were distinguished: in super arid areas with more than 0.67 aridity index, there was constant recharge with little variation with precipitation; in most sites (arid, semi-arid, humid), annual recharge increased as annual precipitation remained above a certain threshold; and in complex areas down to 0.1 aridity index (focused recharge), there was very inconsistent recharge (low precipitation but high recharge). Understanding these relationships can lead to the development of sustainable strategies for water collection. This understanding is particularly crucial in Africa, where water resources are often scarce and climate change poses significant challenges.<ref>{{Citation |title=Global climate change impacts on Sub-Sahara Africa: The case of Nigeria's shorelines |url=http://dx.doi.org/10.3726/978-3-653-04584-0/15 |work=The Impact of Climate Change on Sub-Sahara Africa |date=2015 |access-date=2023-12-19 |publisher=Peter Lang|doi=10.3726/978-3-653-04584-0/15 |isbn=978-3-653-04584-0 }}</ref>

== Water distribution ==

[[File:~~Earth water distribution~~Earth_water_distribution_ppm_chart.svg|thumb|upright=1.3|Visualisation of the distribution (by volume) of water on Earth.{{efn|Each tiny cube{{efn-lr|The entire block comprises 1 million tiny cubes.}} (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~~human-made object).<ref>[http://ga.water.usgs.gov/edu/waterdistribution.html USGS – Earth's water distribution] {{webarchive|url=https://web.archive.org/web/20120629055146/http://ga.water.usgs.gov/edu/waterdistribution.html |date=29 June 2012 }}. Ga.water.usgs.gov (11 December 2012). Retrieved on 29 December 2012.</ref>}}]]
[[File:Earth's_water_distribution.svg|thumb|upright=1.2|A graphical distribution of the locations of water on Earth.{{efn|Only 3% of the Earth's water is fresh water. Most of it is in icecaps and glaciers (69%) and groundwater (30%), while all lakes, rivers and swamps combined only account for a small fraction (0.3%) of the Earth's total freshwater reserves.{{citation needed|date=November 2022}}}}]]

Saline water in [[ocean]]s, [[sea]]s 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 [[glacier]]s, [[ice]] and snow, 0.5–0.75% as fresh groundwater. The water table is the level below which all spaces are filled with water, while the area above this level, where spaces in the rock and soil contain both air and water, is known as the unsaturated zone. The water in this unsaturated zone is referred to as soil moisture.

Saline water in [[ocean]]s, [[sea]]s 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 [[glacier]]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]]s, [[swamp]]s and [[river]]s.<ref>[http://ga.water.usgs.gov/edu/earthwherewater.html Where is Earth's water?] {{webarchive|url=https://web.archive.org/web/20131214091601/http://ga.water.usgs.gov/edu/earthwherewater.html |date=14 December 2013 }}, [[United States Geological Survey]].</ref><ref>[http://www.physicalgeography.net/fundamentals/8b.html Physicalgeography.net] {{webarchive|url=https://web.archive.org/web/20160126072955/http://www.physicalgeography.net/fundamentals/8b.html |date=26 January 2016 }}. Physicalgeography.net. Retrieved on 29 December 2012.</ref> 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.<ref>{{cite book |last= Gleick |first= Peter |author-link=Peter Gleick|editor= Stephen H. Schneider |title= Encyclopedia of Climate and Weather|url= https://archive.org/details/encyclopediaofcl02schn |url-access= registration |publisher= Oxford University Press |year= 1996|display-authors=etal}}</ref> 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]]s. Many areas have very little fresh water, such as [[desert]]s.▼

Below the water table, the entire region is known as the saturated zone, and the water in this zone is called groundwater.<ref name=":0">{{Citation |title=Natural Quality of Water and Groundwater Contamination |date=2000-04-14 |url=http://dx.doi.org/10.1201/9781482278934-9 |work=Groundwater Contamination, Volume I |pages=35–56 |access-date=2023-12-19 |publisher=CRC Press|doi=10.1201/9781482278934-9 |isbn=978-0-429-18165-8 }}</ref> Groundwater plays a crucial role as the primary source of water for various purposes including drinking, washing, farming, and manufacturing, and even when not directly used as a drinking water supply it remains vital to protect due to its ability to carry contaminants and pollutants from the land into lakes and rivers, which constitute a significant percentage of other people's freshwater supply. It is almost ubiquitous underground, residing in the spaces between particles of rock and soil or within crevices and cracks in rock, typically within {{cvt|100|m|ft}} of the surface,<ref name=":0" /> and [[soil]] moisture, and less than 0.01% of it as [[surface water]] in [[lake]]s, [[swamp]]s and [[river]]s.<ref>[http://ga.water.usgs.gov/edu/earthwherewater.html Where is Earth's water?] {{webarchive|url=https://web.archive.org/web/20131214091601/http://ga.water.usgs.gov/edu/earthwherewater.html |date=14 December 2013 }}, [[United States Geological Survey]].</ref><ref>[http://www.physicalgeography.net/fundamentals/8b.html Physicalgeography.net] {{webarchive|url=https://web.archive.org/web/20160126072955/http://www.physicalgeography.net/fundamentals/8b.html |date=26 January 2016 }}. Physicalgeography.net. Retrieved on 29 December 2012.</ref>

▲Saline water in [[ocean]]s, [[sea]]s 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 [[glacier]]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]]s, [[swamp]]s and [[river]]s.<ref>[http://ga.water.usgs.gov/edu/earthwherewater.html Where is Earth's water?] {{webarchive|url=https://web.archive.org/web/20131214091601/http://ga.water.usgs.gov/edu/earthwherewater.html |date=14 December 2013 }}, [[United States Geological Survey]].</ref><ref>[http://www.physicalgeography.net/fundamentals/8b.html Physicalgeography.net] {{webarchive|url=https://web.archive.org/web/20160126072955/http://www.physicalgeography.net/fundamentals/8b.html |date=26 January 2016 }}. Physicalgeography.net. Retrieved on 29 December 2012.</ref> 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.<ref>{{cite book |last= Gleick |first= Peter |author-link=Peter Gleick|editor= Stephen H. Schneider |title= Encyclopedia of Climate and Weather|url= https://archive.org/details/encyclopediaofcl02schn |url-access= registration |publisher= Oxford University Press |year= 1996|display-authors=etal}}</ref> 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]]s. Many areas have very little fresh water, such as [[desert]]s.

== Freshwater ecosystems ==

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{{Further|Human impacts on the environment|Freshwater ecosystem#Threats}}

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 response by [[freshwater ecosystem]]s to a [[Climate change|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.<ref>The World Bank, 2009 {{cite web|title=Water and Climate Change: Understanding the Risks and Making Climate-Smart Investment Decisions|url=http://water.worldbank.org/water/publications/water-and-climate-change-understanding-risks-and-making-climate-smart-investment-decisi|url-status=dead|archive-url=https://web.archive.org/web/20120407105752/http://water.worldbank.org/water/publications/water-and-climate-change-understanding-risks-and-making-climate-smart-investment-decisi/|archive-date=7 April 2012|access-date=24 October 2011|pages=19–22}}</ref>

=== Limited resource ===

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An important concern for hydrological ecosystems is securing minimum [[streamflow]], especially preserving and restoring [[Instream use|instream water allocations]].<ref>{{cite book |title= The world's water, 2006–2007: the biennial report on freshwater resources |author1=Peter Gleick |author-link1=Peter Gleick |author2=Heather Cooley |author3=David Katz |year=2006 |publisher=Island Press |isbn= 978-1-59726-106-7 |pages=29–31 |url= https://books.google.com/books?id=Lttb1qPh4Z8C |access-date=12 September 2009 |archive-date=17 March 2022 |archive-url=https://web.archive.org/web/20220317181510/https://books.google.com/books?id=Lttb1qPh4Z8C |url-status=live }}</ref> Fresh water is an important natural resource necessary for the survival of all [[ecosystem]]s.

===Water pollution===

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=== Global goals for conservation ===

The [[Sustainable Development Goals]] are a collection of 17 interlinked global goals designed to be a "blueprint to achieve a better and more [[Sustainability|sustainable]] future for all".<ref name=":17">United Nations (2017) Resolution adopted by the General Assembly on 6 July 2017, [[:File:A RES 71 313 E.pdf|Work of the Statistical Commission pertaining to the 2030 Agenda for Sustainable Development]] ([https://undocs.org/A/RES/71/313 A/RES/71/313] {{Webarchive|url=https://web.archive.org/web/20201023121826/https://undocs.org/A/RES/71/313 |date=23 October 2020 }})</ref> Targets on ~~freshwater~~fresh [[water conservation]] are included in [[Sustainable Development Goal 6|SDG 6]] (Clean water and sanitation) and [[Sustainable Development Goal 15|SDG 15]] (Life on land). For example, Target 6.4 is formulated as "By 2030, substantially increase [[water-use efficiency]] across all sectors and ensure sustainable withdrawals and [[Water supply|supply of freshwater]] to address water scarcity and substantially reduce the number of people suffering from [[water scarcity]]."<ref name=":17" /> Another target, Target 15.1, is: "By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland [[freshwater ecosystem]]s and their services, in particular forests, [[wetland]]s, [[mountain]]s and [[drylands]], in line with obligations under international agreements."<ref name=":17" />

== See also ==