View source for Earth:Water pollution

{{short description|Contamination of water bodies}}
'''Water pollution''' (or '''aquatic pollution''') is the contamination of [[Earth:Body of water|water bodies]], usually as a result of human activities, so that it negatively affects its uses.<ref name="Von Sperling"/>{{rp|6}} Water bodies include [[Earth:Lake|lake]]s, [[Earth:River|river]]s, [[Earth:Ocean|ocean]]s, [[Earth:Aquifer|aquifer]]s, [[Earth:Reservoir|reservoir]]s and [[Earth:Groundwater|groundwater]]. Water pollution results when contaminants mix with these water bodies. Contaminants can come from one of four main sources: [[Earth:Sewage|sewage]] discharges, industrial activities, agricultural activities, and urban runoff including [[Earth:Stormwater|stormwater]].<ref name=Eckenfelder>{{Cite book |vauthors=Eckenfelder Jr WW |url=https://onlinelibrary.wiley.com/doi/book/10.1002/0471238961 |title=Kirk-Othmer Encyclopedia of Chemical Technology |publisher={{wipe|John Wiley & Sons}} |year=2000 |isbn=978-0-471-48494-3 |doi=10.1002/0471238961.1615121205031105.a01}}</ref> Water pollution is either [[Earth:Surface water|surface water]] pollution or [[Earth:Groundwater pollution|groundwater pollution]]. This form of pollution can lead to many problems, such as the degradation of aquatic ecosystems or spreading water-borne diseases when people use polluted water for drinking or [[Earth:Irrigation|irrigation]].<ref>{{Cite web |date=July 23, 2013 |title=Water Pollution |url=https://www.hsph.harvard.edu/ehep/82-2/ |access-date=September 18, 2021 |website=Environmental Health Education Program |publisher=Harvard T.H. Chan School of Public Health |location=Cambridge, MA |archive-date=September 18, 2021 |archive-url=https://web.archive.org/web/20210918005228/https://www.hsph.harvard.edu/ehep/82-2/ |url-status=live}}</ref> Another problem is that water pollution reduces the [[Biology:Ecosystem service|ecosystem service]]s (such as providing drinking water) that the [[Earth:Water resources|water resource]] would otherwise provide.  

Sources of water pollution are either [[Physics:Point source|point source]]s or non-point sources. Point sources have one identifiable cause, such as a [[Earth:Storm drain|storm drain]], a wastewater treatment plant or an [[Earth:Oil spill|oil spill]]. Non-point sources are more diffuse, such as [[Earth:Surface runoff|agricultural runoff]].<ref name="Moss2008">{{cite journal |vauthors=Moss B |title=Water pollution by agriculture |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=363 |issue=1491 |pages=659–666 |date=February 2008 |pmid=17666391 |pmc=2610176 |doi=10.1098/rstb.2007.2176}}</ref> Pollution is the result of the cumulative effect over time. Pollution may take the form of toxic substances (e.g., oil, metals, plastics, [[Biology:Pesticide|pesticide]]s, persistent organic pollutants, industrial waste products), stressful conditions (e.g., changes of pH, [[Earth:Hypoxia (environmental)|hypoxia]] or anoxia, increased temperatures, excessive [[Biology:Turbidity|turbidity]], changes of [[Earth:Salinity|salinity]]), or the introduction of [[Biology:Pathogen|pathogenic organisms]]. Contaminants may include [[Chemistry:Organic compound|organic]] and inorganic substances. A common cause of [[Physics:Thermal pollution|thermal pollution]] is the use of water as a [[Physics:Coolant|coolant]] by power plants and industrial manufacturers.

Control of water pollution requires appropriate [[Physics:Infrastructure|infrastructure]] and management plans as well as legislation. [[Engineering:Technology|Technology]] solutions can include improving [[Engineering:Sanitation|sanitation]], [[Earth:Sewage treatment|sewage treatment]], [[Earth:Industrial wastewater treatment|industrial wastewater treatment]], agricultural [[Earth:Wastewater treatment|wastewater treatment]], [[Earth:Erosion control|erosion control]], [[Earth:Sediment control|sediment control]] and control of [[Earth:Urban runoff|urban runoff]] (including stormwater management). 

== Definition ==
A practical definition of water pollution is: "Water pollution is the addition of substances or energy forms that directly or indirectly alter the nature of the water body in such a manner that negatively affects its legitimate uses".<ref name="Von Sperling"/>{{rp|6}} Water is typically referred to as polluted when it is impaired by anthropogenic contaminants. Due to these contaminants, it either no longer supports a certain human use, such as drinking water, or undergoes a marked shift in its ability to support its biotic communities, such as fish.

== Contaminants ==

===Contaminants with an origin in sewage ===

The following compounds can all reach water bodies via raw sewage or even treated sewage discharges:
* Various chemical compounds found in personal hygiene and cosmetic products.
* [[Earth:Disinfection by-product|Disinfection by-product]]s found in chemically disinfected drinking water (whilst these chemicals can be a pollutant in the [[Engineering:Water distribution system|water distribution network]], they are fairly volatile and therefore not usually found in environmental waters).<ref>{{cite journal |vauthors=Alexandrou L, Meehan BJ, Jones OA |title=Regulated and emerging disinfection by-products in recycled waters |journal=The Science of the Total Environment |volume=637–638 |pages=1607–1616 |date=October 2018 |pmid=29925195 |doi=10.1016/j.scitotenv.2018.04.391 |bibcode=2018ScTEn.637.1607A |s2cid=49355478}}</ref>
* [[Biology:Hormone|Hormone]]s (from animal husbandry and residue from human [[Chemistry:Hormonal contraception|hormonal contraception]] methods) and synthetic materials such as [[Chemistry:Phthalate|phthalate]]s that mimic hormones in their action. These can have adverse impacts even at very low concentrations on the natural biota and potentially on humans if the water is treated and utilized for drinking water.<ref>{{cite web |title=Environment Agency (archive) – Persistent, bioaccumulative and toxic PBT substances |url=http://www.environment-agency.gov.uk/business/444304/1290036/1290100/1290353/1294402/1311542/?version=1&lang=_e |archive-url=https://web.archive.org/web/20060804195610/http://www.environment-agency.gov.uk/business/444304/1290036/1290100/1290353/1294402/1311542/?version=1&lang=_e |archive-date=August 4, 2006 |access-date=2012-11-14 |publisher=Environment Agency (UK)}}</ref><ref>[http://planetearth.nerc.ac.uk/news/story.aspx?id=297 Natural Environmental Research Council – River sewage pollution found to be disrupting fish hormones] {{Webarchive|url=https://web.archive.org/web/20150427112251/http://planetearth.nerc.ac.uk/news/story.aspx?id=297 |date=April 27, 2015 }}. Planetearth.nerc.ac.uk. Retrieved on 2012-12-19.</ref><ref>{{cite web |title=Endocrine Disruption Found in Fish Exposed to Municipal Wastewater |url=http://toxics.usgs.gov/highlights/wastewater_fish.html |archive-url=https://web.archive.org/web/20111015161223/http://toxics.usgs.gov/highlights/wastewater_fish.html |archive-date=October 15, 2011 |access-date=2012-11-14 |publisher=US Geological Survey |location=Reston, VA}}</ref>
* [[Biology:Insecticide|insecticide]]s and [[Biology:Herbicide|herbicide]]s, often from agricultural runoff.
If the water pollution stems from sewage (municipal wastewater), the main pollutants are: suspended solids, biodegradable organic matter, nutrients and pathogenic (disease-causing) organisms.<ref name="Von Sperling"/>{{rp|6}} [[File:South Asia Poster 03.jpg|thumb|Poster to teach people in South Asia about human activities leading to the pollution of water sources]]

{| class="wikitable"
|+Pollutants and their effects*
!Pollutant
!Main representative parameter
!Possible effect of the pollutant
|-
|[[Chemistry:Suspended solids|Suspended solids]]
|[[Earth:Total suspended solids|Total suspended solids]]
|
* [[Social:Aesthetics|Aesthetic]] problems
* [[Engineering:Sludge|Sludge]] deposits
* Pollutants [[Chemistry:Adsorption|adsorption]]
* Protection of pathogens
|-
|Biodegradable organic matter
|[[Chemistry:Biochemical oxygen demand|Biological oxygen demand]] (BOD)
|
* Oxygen consumption
* Death of fish
* Septic conditions
|-
|[[Earth:Nutrient|Nutrient]]s
|
* [[Chemistry:Nitrogen|Nitrogen]]
* [[Chemistry:Phosphorus|Phosphorus]]
|
* [[Earth:Harmful algal bloom|Excessive algae growth]]
* Toxicity to fish ([[Chemistry:Ammonia|ammonia]])
* Illnesses in new-born infants ([[Medicine:Blue baby syndrome|Blue baby syndrome]] from [[Chemistry:Nitrate|nitrate]])
* [[Earth:Groundwater pollution|Pollution of groundwater]]
|-
|Pathogens
|
* Coliforms, such as [[Biology:Escherichia coli|E. coli]]
* Helminth eggs<ref name="World Health Organization">{{cite book |url=http://www.susana.org/en/resources/library/details/1004|title=Guidelines for the Safe Use of Wastewater, Excreta and Greywater, Volume 4 Excreta and Greywater Use in Agriculture |date=2006 |publisher=[[Organization:World Health Organization|World Health Organization]] |isbn=92-4-154685-9 |edition=third |location=Geneva}}</ref>
|Waterborne diseases
|-
|Non-biodegradable organic matter
|
* [[Biology:Pesticide|Pesticide]]s
* Some detergents
* Others
|
* [[Medicine:Toxicity|Toxicity]] (various)
* Foam (detergents)
* Reduction of oxygen transfer (detergents)
* Non-biodegradability
* Bad [[Chemistry:Odor|odor]]s (e.g.: [[Chemistry:Phenols|phenols]])
|-
|Inorganic dissolved solids
|
* [[Earth:Total dissolved solids|Total dissolved solids]]
* [[Physics:Conductivity (electrolytic)|Conductivity]]
|
* Excessive [[Earth:Salinity|salinity]] – harm to plantations ([[Earth:Irrigation|irrigation]])
* Toxicity to plants (some ions)
* Problems with [[Earth:Permeability (Earth sciences)|soil permeability]] ([[Chemistry:Sodium|sodium]])
|-
| colspan=3 style="text-align: left;" |* Sources of these pollutants are municipal and industrial wastewater, urban runoff, agricultural and pasture activities<ref name="Von Sperling" />{{rp|7}}
|}

==== Pathogens ====
The major groups of pathogenic organisms are: (a) bacteria, (b) viruses, (c) protozoans and (d) helminths.<ref name="Von Sperling"/>{{rp|47}} In practice, [[Biology:Indicator organism|indicator organism]]s are used to investigate pathogenic pollution of water because the detection of pathogenic organisms in water sample is difficult and costly, because of their low concentrations. The indicators ([[Earth:Indicator bacteria|bacterial indicator]]) of fecal contamination of water samples most commonly used are: total coliforms (TC), fecal coliforms (FC) or thermotolerant coliforms, E. coli.<ref name="Von Sperling"/>{{rp|47}}

Pathogens can produce waterborne diseases in either human or animal hosts.<ref>{{Cite book |url=https://pubs.rsc.org/en/content/ebook/978-1-84973-648-0 |title=Pollution: Causes, effects, and control |date=2013 |publisher=[[Organization:Royal Society of Chemistry|Royal Society of Chemistry]] |vauthors=Harrison RM |editor-first1=R. M. |editor-last1=Harrison |isbn=978-1-78262-560-5 |edition=5th |location=Cambridge, UK |doi=10.1039/9781782626527 |oclc=1007100256}}</ref> Some microorganisms sometimes found in contaminated surface waters that have caused human health problems include: ''[[Biology:Burkholderia pseudomallei|Burkholderia pseudomallei]],'' ''[[Biology:Cryptosporidium parvum|Cryptosporidium parvum]],'' ''[[Biology:Giardia lamblia|Giardia lamblia]],'' ''[[Biology:Salmonella|Salmonella]],'' [[Medicine:Norovirus|norovirus]] and other viruses, parasitic worms including the ''[[Biology:Schistosoma|Schistosoma]]'' type.''<ref>Schueler, Thomas R. "Microbes and Urban Watersheds: Concentrations, Sources, & Pathways." Reprinted in [http://cwp.org/documents/cat_view/75-articles-from-the-practice-of-watershed-protection.html?limit=40&order=name&dir=DESC&start=80 ''The Practice of Watershed Protection.''] {{webarchive|url=https://web.archive.org/web/20130108194041/http://www.cwp.org/documents/cat_view/75-articles-from-the-practice-of-watershed-protection.html?limit=40&order=name&dir=DESC&start=80 |date=January 8, 2013}} 2000. Center for Watershed Protection. Ellicott City, MD.</ref>''

The source of high levels of pathogens in water bodies can be from [[Medicine:Human feces|human feces]] (due to open defecation), sewage, [[Earth:Blackwater (waste)|blackwater]], or [[Chemistry:Manure|manure]] that has found its way into the water body. The cause for this can be lack of sanitation procedures or poorly functioning on-site [[Engineering:Sanitation|sanitation]] systems ([[Engineering:Septic tank|septic tank]]s, [[Engineering:Pit latrine|pit latrine]]s), [[Earth:Sewage treatment|sewage treatment plants]] without disinfection steps, [[Earth:Sanitary sewer overflow|sanitary sewer overflow]]s and combined sewer overflows (CSOs)<ref name="EPARTC">{{cite report |url=https://www.epa.gov/npdes/2004-npdes-cso-report-congress |title=Report to Congress: Impacts and Control of CSOs and SSOs |date=August 2004 |publisher=EPA |id=EPA 833-R-04-001}}</ref> during storm events and intensive agriculture (poorly managed livestock operations).

=== Organic compounds ===
Organic substances that enter water bodies are often toxic.<ref name="Laws-aquatic">{{cite book |vauthors=Laws EA |url=https://books.google.com/books?id=V5D2DQAAQBAJ |title=Aquatic Pollution<nowiki>:</nowiki> An Introductory Text |date=2018 |publisher={{wipe|John Wiley & Sons}} |isbn=978-1-119-30450-0 |edition=4th |location=Hoboken, NJ |via=[[Google Books]]}}</ref>{{rp|229}}
* [[Chemistry:Petroleum|Petroleum]] hydrocarbons, including fuels ([[Chemistry:Gasoline|gasoline]], [[Chemistry:Diesel fuel|diesel fuel]], jet fuels, and [[Chemistry:Fuel oil|fuel oil]]) and lubricants (motor oil), and fuel [[Physics:Combustion|combustion]] byproducts, from [[Earth:Oil spill|oil spill]]s or [[Earth:Stormwater|storm water]] runoff<ref name="Burton & Pitt">{{cite book |url=http://unix.eng.ua.edu/~rpitt/Publications/BooksandReports/Stormwater%20Effects%20Handbook%20by%20%20Burton%20and%20Pitt%20book/MainEDFS_Book.html |title=Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers |chapter=2 |publisher=CRC/Lewis Publishers |year=2001 |isbn=0-87371-924-7 |location=New York |vauthors=Burton Jr GA, Pitt R |access-date=January 26, 2009 |archive-date=May 19, 2009 |archive-url=https://web.archive.org/web/20090519035716/http://unix.eng.ua.edu/~rpitt/Publications/BooksandReports/Stormwater%20Effects%20Handbook%20by%20%20Burton%20and%20Pitt%20book/MainEDFS_Book.html |url-status=dead}}</ref>
* Volatile organic compounds, such as improperly stored industrial [[Physics:Solvent|solvent]]s. Problematic species are [[Chemistry:Organochloride|organochloride]]s such as [[Chemistry:Polychlorinated biphenyl|polychlorinated biphenyl]] (PCBs) and [[Chemistry:Trichloroethylene|trichloroethylene]], a common solvent.

[[Chemistry:Per- and polyfluoroalkyl substances|Per- and polyfluoroalkyl substances]] (PFAS) are persistent organic pollutants.<ref name="ReferenceA">{{cite journal |vauthors = Johnson MS, Buck RC, Cousins IT, Weis CP, Fenton SE |title=Estimating Environmental Hazard and Risks from Exposure to Per- and Polyfluoroalkyl Substances (PFASs): Outcome of a SETAC Focused Topic Meeting |journal=[[Chemistry:Environmental Toxicology and Chemistry|Environmental Toxicology and Chemistry]] |volume=40 |issue=3 |pages=543–549 |date=March 2021 |pmid=32452041 |pmc=8387100 |doi=10.1002/etc.4784}}</ref><ref name="linkinghub.elsevier.com">{{cite journal |vauthors=Sinclair GM, Long SM, Jones OA |title=What are the effects of PFAS exposure at environmentally relevant concentrations? |journal=Chemosphere |volume=258 |pages=127340 |date=November 2020 |pmid=32563917 |doi=10.1016/j.chemosphere.2020.127340 |s2cid=219974801 |bibcode=2020Chmsp.258l7340S}}</ref>

=== Inorganic contaminants ===
[[File:Bützflethermoor Rotschlammdeponie Luftaufnahmen 2012-05-by-RaBoe-478-1.jpg|thumb|[[Earth:Red mud|Bauxite residue]] is an industrial waste that is dangerously alkaline and can lead to water pollution if not managed appropriately (photo from Stade, Germany).]]
[[File:muddy USGS.jpg|thumb|right|Muddy river polluted by sediment]]
Inorganic water pollutants include for example:
* [[Chemistry:Ammonia|Ammonia]] from food processing waste
* [[Chemistry:Heavy metals|Heavy metals]] from motor vehicles (via [[Earth:Urban runoff|urban storm water runoff]])<ref name="Burton & Pitt" /><ref>Schueler, Thomas R. "Cars Are Leading Source of Metal Loads in California." Reprinted in [http://cwp.org/documents/cat_view/75-articles-from-the-practice-of-watershed-protection.html ''The Practice of Watershed Protection.''] {{webarchive|url=https://web.archive.org/web/20120312045934/http://www.cwp.org/documents/cat_view/75-articles-from-the-practice-of-watershed-protection.html|date=March 12, 2012}} 2000. Center for Watershed Protection. Ellicott City, MD.</ref> and acid mine drainage
* Nitrates and [[Chemistry:Phosphate|phosphate]]s, from sewage and agriculture (''see'' [[Earth:Nutrient pollution|nutrient pollution]])
* [[Earth:Silt|Silt]] ([[Earth:Sediment|sediment]]) in runoff from construction sites or sewage, logging, slash and burn practices or land clearing sites.
* Salt: [[Earth:Freshwater salinization|Freshwater salinization]] is the process of salty runoff contaminating [[Earth:Freshwater ecosystem|freshwater ecosystem]]s.<ref name="Kaushal et al">{{cite journal |vauthors=Kaushal SS, Likens GE, Pace ML, Utz RM, Haq S, Gorman J, Grese M |title=Freshwater salinization syndrome on a continental scale |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=115 |issue=4 |pages=E574–E583 |date=January 2018 |pmid=29311318 |pmc=5789913 |doi=10.1073/pnas.1711234115 |bibcode=2018PNAS..115E.574K |doi-access=free}}</ref> Human-induced salinization is termed as secondary salinization, with the use of [[Chemistry:De-icing|de-icing]] road salts as the most common form of runoff.<ref>{{cite journal |vauthors=Evans DM, Villamagna AM, Green MB, Campbell JL |title=Origins of stream salinization in an upland New England watershed |journal=Environmental Monitoring and Assessment |volume=190 |issue=9 |pages=523 |date=August 2018 |pmid=30116969 |doi=10.1007/s10661-018-6802-4 |bibcode=2018EMnAs.190..523E |s2cid=52022441}}</ref><ref name="Cañedo-Argüelles">{{cite journal |vauthors=Cañedo-Argüelles M, Kefford B, Schäfer R |title=Salt in freshwaters: causes, effects and prospects - introduction to the theme issue |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=374 |issue=1764 |date=December 2018 |pmid=30509904 |pmc=6283966 |doi=10.1098/rstb.2018.0002}}</ref>

=== Pharmaceutical pollutants ===
{{excerpt|Environmental impact of pharmaceuticals and personal care products|paragraphs=1-3|file=no}}
* [[Medicine:Environmental persistent pharmaceutical pollutant|Environmental persistent pharmaceutical pollutant]]s, which can include various pharmaceutical drugs and their [[Biology:Metabolite|metabolite]]s (''see also'' [[Chemistry:Drug pollution|drug pollution]]), such as [[Chemistry:Antidepressant|antidepressant]] drugs, [[Chemistry:Antibiotic|antibiotic]]s or the contraceptive pill.
* Metabolites of [[Finance:Illegal drug trade|illicit drugs]] (see also [[Medicine:Wastewater-based epidemiology|wastewater epidemiology]]), for example [[Chemistry:Methamphetamine|methamphetamine]] and [[Chemistry:MDMA|ecstasy.]]<ref>{{Cite journal |vauthors=Knight K |date=2021 |title=Freshwater methamphetamine pollution turns brown trout into addicts |url=https://journals.biologists.com/jeb/article/224/13/jeb242971/270754/Freshwater-methamphetamine-pollution-turns-brown |journal=Journal of Experimental Biology |volume=224 |issue=13 |pages=jeb242971 |doi=10.1242/jeb.242971 |issn=0022-0949 |doi-access=free}}</ref><ref name="De Lorenzo">{{Cite web |last=De Lorenzo |first=D |title=MDMA Gangs Are Literally Polluting Europe |url=https://www.vice.com/en/article/qj83jw/mdma-gangs-are-literally-polluting-europe |date=2021-06-18 |website=Vice World News |publisher=Vice Media Group |location=Brooklyn, NY}}</ref>

=== Solid waste and plastics ===
[[File:Canal-pollution.jpg|thumb|Solid waste and plastics in the Lachine Canal, Canada]]

Solid waste can enter water bodies through untreated sewage, combined sewer overflows, urban runoff, people discarding garbage into the environment, wind carrying municipal solid waste from landfills and so forth. This results in [[Physics:Macroscopic scale|macroscopic]] pollution– large visible items polluting the water– but also [[Earth:Microplastics|microplastics]] pollution that is not directly visible. The terms [[Earth:Marine debris|marine debris]] and [[Earth:Marine plastic pollution|marine plastic pollution]] are used in the context of pollution of oceans.

Microplastics persist in the environment at high levels, particularly in [[Earth:Aquatic ecosystem|aquatic]] and [[Earth:Marine ecosystem|marine ecosystem]]s, where they cause water pollution.<ref name=":9">{{Cite web |title=Development solutions: Building a better ocean |url=https://www.eib.org/en/essays/plastic-pollution |access-date=2020-08-19 |website=European Investment Bank}}</ref> 35% of all ocean microplastics come from textiles/clothing, primarily due to the erosion of polyester, acrylic, or nylon-based clothing, often during the washing process.<ref>{{Cite web |vauthors=Resnick B |date=2018-09-19 |title=More than ever, our clothes are made of plastic. Just washing them can pollute the oceans |url=https://www.vox.com/the-goods/2018/9/19/17800654/clothes-plastic-pollution-polyester-washing-machine |access-date=2021-10-04 |website=Vox}}</ref> 

Stormwater, untreated sewage and wind are the primary conduits for microplastics from land to sea. Synthetic fabrics, tyres, and city dust are the most common sources of microplastics. These three sources account for more than 80% of all microplastic contamination.<ref name=":0">{{Cite journal |last=Bank |first=European Investment |date=2023-02-27 |title=Microplastics and Micropollutants in Water: Contaminants of Emerging Concern |url=https://www.eib.org/en/publications/20230042-microplastics-and-micropollutants-in-water |language=EN}}</ref><ref>{{Cite web |title=Microplastics from textiles: towards a circular economy for textiles in Europe — European Environment Agency |url=https://www.eea.europa.eu/publications/microplastics-from-textiles-towards-a |access-date=2023-03-24 |website=www.eea.europa.eu |language=en}}</ref>

== Types of surface water pollution ==
Surface water pollution includes pollution of rivers, lakes and oceans. A subset of surface water pollution is [[Earth:Marine pollution|marine pollution]] which affects the oceans. [[Earth:Nutrient pollution|Nutrient pollution]] refers to contamination by excessive inputs of nutrients.

Globally, about 4.5&nbsp;billion people do not have [[Engineering:Improved sanitation|safely managed sanitation]] as of 2017, according to an estimate by the Joint Monitoring Programme for Water Supply and Sanitation.<ref name="JMP2017">WHO and UNICEF (2017) [https://washdata.org/reports Progress on Drinking Water, Sanitation and Hygiene: 2017 Update and SDG Baselines]. Geneva: World Health Organization (WHO) and the United Nations Children's Fund (UNICEF), 2017</ref> Lack of access to sanitation is concerning and often leads to water pollution, e.g. via the practice of open defecation: during rain events or floods, the [[Medicine:Human feces|human feces]] are moved from the ground where they were deposited into surface waters. Simple pit latrines may also get flooded during rain events.

As of 2022, [[Earth:Europe|Europe]] and [[Place:Central Asia|Central Asia]] account for around 16% of global microplastics discharge into the seas.<ref>{{Cite journal |last1=Ritchie |first1=Hannah |last2=Roser |first2=Max |date=2018-09-01 |title=Plastic Pollution |url=https://ourworldindata.org/plastic-pollution |journal=Our World in Data}}</ref><ref name=":0" /><ref>{{Cite web |last=Ferris |first=Robert |title=Half of plastic trash in oceans comes from 5 countries |url=https://www.cnbc.com/2016/01/13/half-of-plastic-trash-in-oceans-comes-from-5-countries.html |access-date=2023-03-24 |website=CNBC |date=January 13, 2016 |language=en}}</ref>

=== Marine pollution ===
{{Excerpt|Marine pollution|paragraphs=1|file=no}}

=== Nutrient pollution ===
{{Excerpt|Nutrient pollution|paragraphs=1|file=no}}

===Thermal pollution===
[[File:Brayton Point Power Station.JPG|thumb|The Brayton Point Power Station in Massachusetts discharges heated water to Mount Hope Bay.]]
{{excerpt|Thermal pollution|paragraphs=1|file=no}}
Elevated water temperatures decrease [[Chemistry:Oxygen|oxygen]] levels (due to lower levels of dissolved oxygen, as gases are less soluble in warmer liquids), which can kill fish (which may then rot) and alter food chain composition, reduce species [[Biology:Biodiversity|biodiversity]], and foster invasion by new thermophilic species.<ref>{{Cite book |vauthors=Goel PK |url=https://www.worldcat.org/oclc/85857626|title=Water pollution: causes, effects and control |date=2006 |publisher=New Age International |isbn=81-224-1839-2 |edition=Rev. 2nd |location=New Delhi |oclc=85857626}}</ref>{{rp|179}}<ref name="Laws-aquatic" />{{rp|375}}

=== Biological pollution ===
The introduction of aquatic [[Earth:Invasive species|invasive organisms]] is a form of water pollution as well. It causes [[Biology:Biological pollution|biological pollution]].<ref>{{cite journal |vauthors=Olenin S, Minchin D, Daunys D |title=Assessment of biopollution in aquatic ecosystems |journal=Marine Pollution Bulletin |volume=55 |issue=7–9 |pages=379–394 |date=2007 |pmid=17335857 |doi=10.1016/j.marpolbul.2007.01.010|bibcode=2007MarPB..55..379O }}</ref>

== Groundwater pollution ==
{{excerpt|Groundwater pollution|paragraphs=1|file=no}}In many areas of the world, groundwater pollution poses a hazard to the wellbeing of people and ecosystems. One-quarter of the world's population depends on groundwater for drinking, yet concentrated recharging is known to carry short-lived contaminants into carbonate aquifers and jeopardize the purity of those waters.<ref>{{Cite journal |last1=Hartmann |first1=Andreas |last2=Jasechko |first2=Scott |last3=Gleeson |first3=Tom |last4=Wada |first4=Yoshihide |last5=Andreo |first5=Bartolomé |last6=Barberá |first6=Juan Antonio |last7=Brielmann |first7=Heike |last8=Bouchaou |first8=Lhoussaine |last9=Charlier |first9=Jean-Baptiste |last10=Darling |first10=W. George |last11=Filippini |first11=Maria |date=2021-05-18 |title=Risk of groundwater contamination widely underestimated because of fast flow into aquifers |journal=Proceedings of the National Academy of Sciences |language=en |volume=118 |issue=20 |pages=e2024492118 |doi=10.1073/pnas.2024492118 |issn=0027-8424 |pmc=8158018 |pmid=33972438|bibcode=2021PNAS..11824492H|doi-access=free }}</ref>

== Pollution from point sources ==
Point source water pollution refers to contaminants that enter a waterway from a single, identifiable source, such as a pipe or ditch. Examples of sources in this category include discharges from a sewage treatment plant, a factory, or a city [[Earth:Storm drain|storm drain]].

The U.S. Clean Water Act (CWA) defines point source for regulatory enforcement purposes (''see'' United States regulation of point source water pollution).<ref>United States. Clean Water Act (CWA), section 502(14), {{USC|33|1362}} (14).</ref> The CWA definition of point source was amended in 1987 to include municipal storm sewer systems, as well as industrial storm water, such as from construction sites.<ref>U.S. CWA section 402(p), {{USC|33|1342(p)}}</ref>

=== Sewage ===
Sewage typically consists of 99.9% water and 0.1% solids.<ref>{{cite book |vauthors=Scholz M |title=Wetlands for Water Pollution Control |year=2016 |isbn=978-0-444-63607-2 |pages=13–15 |chapter=Sewage Treatment |doi=10.1016/B978-0-444-63607-2.00003-4}}</ref> Sewage contributes many classes of nutrients that lead to eutrophication. It is a major source of phosphate for example.<ref name="WPC2">{{cite book |title=Water Pollution Control |year=2014 |isbn=978-1-118-86383-1 |veditors=Nesaratnam ST |doi=10.1002/9781118863831}}</ref> Sewage is often contaminated with diverse compounds found in personal hygiene, cosmetics, pharmaceutical drugs (see also [[Chemistry:Drug pollution|drug pollution]]), and their metabolites<ref>{{Cite journal |vauthors=Knight K |date=2021 |title=Freshwater methamphetamine pollution turns brown trout into addicts |url=https://journals.biologists.com/jeb/article/224/13/jeb242971/270754/Freshwater-methamphetamine-pollution-turns-brown |journal=Journal of Experimental Biology |volume=224 |issue=13 |pages=jeb242971 |doi=10.1242/jeb.242971 |issn=0022-0949 |doi-access=free}}</ref><ref name="De Lorenzo"/> Water pollution due to environmental persistent pharmaceutical pollutants can have wide-ranging consequences. When sewers overflow during storm events this can lead to water pollution from untreated sewage. Such events are called [[Earth:Sanitary sewer overflow|sanitary sewer overflow]]s or [[Earth:Combined sewer|combined sewer overflows]].[[File:AngleseyCopperStream.jpg|thumb|upright|A polluted river draining an abandoned copper mine on Anglesey]]

=== Industrial wastewater ===
[[File:Perfluorooctanesulfonic acid.svg|thumb|right|[[Chemistry:Perfluorooctanesulfonic acid|Perfluorooctanesulfonic acid]] (PFOS) is a global pollutant that has been found in drinking water. It appears not to biodegrade.<ref name="PR09May">{{Cite web |url=http://chm.pops.int/Convention/Pressrelease/COP4Geneva8May2009/tabid/542/language/en-US/Default.aspx |title=Governments unite to step-up reduction on global DDT reliance and add nine new chemicals under international treaty |date=8 May 2009 |publisher=Stockholm Convention Secretariat |location=Geneva |id=Press release}}</ref>]]{{Further|Industrial wastewater treatment}}

Industrial processes that use water also produce wastewater. This is called [[Earth:Industrial wastewater treatment|industrial wastewater]]. Using the US as an example, the main industrial consumers of water (using over 60% of the total consumption) are power plants, petroleum refineries, iron and steel mills, pulp and paper mills, and food processing industries.<ref name=Eckenfelder/> Some industries discharge chemical wastes, including solvents and heavy metals (which are toxic) and other harmful pollutants. 

<section begin=Pollutants in industrial wastewater/>Industrial wastewater could add the following pollutants to receiving water bodies if the wastewater is not treated and managed properly:
* [[Chemistry:Toxic heavy metal|Heavy metals]], including [[Chemistry:Mercury (element)|mercury]], [[Chemistry:Lead|lead]], and [[Chemistry:Chromium|chromium]]
* Organic matter and nutrients such as food waste: Certain industries (e.g. [[Engineering:Food processing|food processing]], slaughterhouse waste, paper fibers, plant material, etc.) discharge high concentrations of BOD, ammonia nitrogen and oil and grease.<ref>{{Cite book |url=https://www.worldcat.org/oclc/48053912 |title=Wastewater engineering: treatment and reuse |date=2003 |publisher=McGraw-Hill |vauthors=Tchobanoglous G, Burton FL, Stensel HD |isbn=0-07-041878-0 |edition=4th |location=Boston |chapter=Chapter 3: Analysis and Selection of Wastewater Flowrates and Constituent Loadings |oclc=48053912}}</ref>{{rp|180}}<ref name="Laws-aquatic" /> 
* Inorganic particles such as sand, grit, metal particles, rubber residues from tires, ceramics, etc.;
* Toxins such as [[Biology:Pesticide|pesticide]]s, [[Chemistry:Poison|poison]]s, [[Biology:Herbicide|herbicide]]s, etc.
* Pharmaceuticals, endocrine disrupting compounds, hormones, perfluorinated compounds, siloxanes, drugs of abuse and other hazardous substances<ref name="pmid25889547">{{cite journal |vauthors=Arvaniti OS, Stasinakis AS |title=Review on the occurrence, fate and removal of perfluorinated compounds during wastewater treatment |journal=The Science of the Total Environment |volume=524–525 |issue= |pages=81–92 |date=August 2015 |pmid=25889547 |doi=10.1016/j.scitotenv.2015.04.023 |bibcode=2015ScTEn.524...81A}}</ref><ref name="pmid23320453">{{cite journal |vauthors=Bletsou AA, Asimakopoulos AG, Stasinakis AS, Thomaidis NS, Kannan K |title=Mass loading and fate of linear and cyclic siloxanes in a wastewater treatment plant in Greece |journal=Environmental Science & Technology |volume=47 |issue=4 |pages=1824–32 |date=February 2013 |pmid=23320453 |doi=10.1021/es304369b |bibcode=2013EnST...47.1824B |s2cid=39997737}}</ref><ref name="pmid27236142">{{cite journal |vauthors=Gatidou G, Kinyua J, van Nuijs AL, Gracia-Lor E, Castiglioni S, Covaci A, Stasinakis AS |title=Drugs of abuse and alcohol consumption among different groups of population on the Greek Island of Lesvos through sewage-based epidemiology |journal=The Science of the Total Environment |volume=563–564 |issue= |pages=633–40 |date=September 2016 |pmid=27236142 |doi=10.1016/j.scitotenv.2016.04.130 |bibcode=2016ScTEn.563..633G |hdl=10067/1345920151162165141|s2cid=4073701 |hdl-access=free }}</ref>
* [[Earth:Microplastics|Microplastics]] such as polyethylene and polypropylene beads, polyester and polyamide<ref name="pmid30620926">{{cite journal |vauthors=Gatidou G, Arvaniti OS, Stasinakis AS |title=Review on the occurrence and fate of microplastics in Sewage Treatment Plants |journal=[[Physics:Journal of Hazardous Materials|Journal of Hazardous Materials]] |volume=367 |issue= |pages=504–512 |date=April 2019 |pmid=30620926 |doi=10.1016/j.jhazmat.2018.12.081 |s2cid=58567561}}</ref>
* [[Physics:Thermal pollution|Thermal pollution]] from [[Chemistry:Power station|power station]]s and industrial manufacturers
* [[Physics:Radionuclide|Radionuclide]]s from [[Physics:Uranium mining|uranium mining]], processing [[Physics:Nuclear fuel|nuclear fuel]], operating [[Physics:Nuclear reactor|nuclear reactor]]s, or disposal of [[Physics:Radioactive waste|radioactive waste]].
* Some industrial discharges include persistent organic pollutants such as [[Chemistry:Per- and polyfluoroalkyl substances|per- and polyfluoroalkyl substances]] (PFAS).<ref name="ReferenceA" /><ref name="linkinghub.elsevier.com" /><section end=Pollutants in industrial wastewater/>

=== Oil spills ===
{{Excerpt|Oil spill|paragraphs=1|file=no}}
== Pollution from nonpoint sources ==
{{Excerpt|Nonpoint source pollution|paragraphs=1|file=no}}

=== Agriculture ===
Agriculture is a major contributor to water pollution from nonpoint sources. The use of fertilizers as well as [[Earth:Surface runoff|surface runoff]] from farm fields, pastures and feedlots leads to nutrient pollution.<ref>{{Cite book |veditors=Walters A |title=Nutrient Pollution From Agricultural Production: Overview, Management and a Study of Chesapeake Bay |url=https://novapublishers.com/shop/nutrient-pollution-from-agricultural-production-overview-management-and-a-study-of-chesapeake-bay/ |date=2016 |publisher=Nova Science Publishers |location=Hauppauge, NY |isbn=978-1-63485-188-6 |oclc=960163923}}</ref> In addition to plant-focused agriculture, fish-farming is also a source of pollution. Additionally, agricultural runoff often contains high levels of pesticides.<ref name=Eckenfelder/>

=== Atmospheric contributions (air pollution) ===
Air deposition is a process whereby air pollutants from industrial or natural sources settle into water bodies. The deposition may lead to polluted water near the source, or at distances up to a few thousand miles away. The most frequently observed water pollutants resulting from industrial air deposition are sulfur compounds, nitrogen compounds, mercury compounds, other heavy metals, and some pesticides and industrial by-products. Natural sources of air deposition include forest fires and microbial activity.<ref name="EPA air deposition">{{cite report |title=Frequently Asked Questions About Air Deposition |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=2000NQU1.txt |date=September 2001 |pages=3–7 |publisher=EPA |id=EPA 453/R-01-009}}</ref>

[[Earth:Acid rain|Acid rain]] is caused by emissions of [[Chemistry:Sulfur dioxide|sulfur dioxide]] and [[Chemistry:Nitrogen oxide|nitrogen oxide]], which react with the [[Chemistry:Properties of water|water molecules]] in the [[Astronomy:Atmosphere|atmosphere]] to produce acids.<ref name=":5">{{Cite web |date=2022-06-24 |title=What is Acid Rain? |url=https://www.epa.gov/acidrain/what-acid-rain |publisher=EPA}}</ref> Some governments have made efforts since the 1970s to reduce the release of sulfur dioxide and nitrogen oxide into the atmosphere. The main source of sulfur and nitrogen compounds that result in acid rain are anthropogenic, but nitrogen oxides can also be produced naturally by [[Astronomy:Lightning|lightning]] strikes and sulphur dioxide is produced by [[Earth:Types of volcanic eruptions|volcanic eruptions]].<ref>{{Cite journal |vauthors=Sisterson DL, Liaw YP |date=1990-01-01 |title=An evaluation of lightning and corona discharge on thunderstorm air and precipitation chemistry |journal=Journal of Atmospheric Chemistry |volume=10 |issue=1 |pages=83–96 |bibcode=1990JAtC...10...83S |doi=10.1007/BF01980039 |issn=1573-0662 |s2cid=97714446}}</ref> Acid rain can have harmful effects on plants, aquatic ecosystems and infrastructure.<ref>{{Cite web |date=2022-04-24 |title=Effects of Acid Rain |url=https://www.epa.gov/acidrain/effects-acid-rain |publisher=EPA}}</ref><ref name=":6">{{cite book |vauthors=Kjellstrom T, Lodh M, McMichael T, Ranmuthugala G, Shrestha R, Kingsland S |chapter=Air and Water Pollution: Burden and Strategies for Control |date=2006 |chapter-url=http://www.ncbi.nlm.nih.gov/books/NBK11769/ |title= Disease Control Priorities in Developing Countries |veditors=Jamison DT, Breman JG, Measham AR, Alleyne G, Claeson M, Evans DB, Jha P, Mills A, Musgrove P |archive-url=https://web.archive.org/web/20200807014923/https://www.ncbi.nlm.nih.gov/books/NBK11769/ |edition=2nd |publisher=World Bank |isbn=978-0-8213-6179-5 |pmid=21250344 |archive-date=August 7, 2020 |url-status=live}}</ref>

[[Earth:Carbon dioxide in Earth's atmosphere|Carbon dioxide concentrations in the atmosphere]] have increased since the 1850s due anthropogenic influences ([[Earth:Greenhouse gas emissions|emissions of greenhouse gases]]).<ref name="cald03" /> This leads to [[Biology:Ocean acidification|ocean acidification]] and is another form of water pollution from atmospheric contributions.<ref>{{cite journal |vauthors=Doney SC, Fabry VJ, Feely RA, Kleypas JA |title=Ocean acidification: the other CO2 problem |journal=Annual Review of Marine Science |volume=1 |issue=1 |pages=169–192 |date=2009-01-01 |pmid=21141034 |doi=10.1146/annurev.marine.010908.163834 |bibcode=2009ARMS....1..169D|s2cid=402398 }}</ref>

== Sampling, measurements, analysis ==
[[File:Research- water sampling equipment.jpg|thumb|right|[[Environmental science|Environmental scientists]] preparing water autosamplers]]

Water pollution may be analyzed through several broad categories of methods: physical, chemical and biological. Some methods may be conducted ''[[Biology:In situ|in situ]]'', without sampling, such as temperature. Others involve collection of samples, followed by specialized analytical tests in the laboratory. Standardized, validated analytical test methods, for water and wastewater samples have been published.<ref>For example, see {{cite book |title=Standard Methods For the Examination of Water and Wastewater |edition=21 |editor-last1=Eaton |editor-first1=Andrew D. |editor-last2=Greenberg |editor-first2=Arnold E. |editor-last3=Rice |editor-first3=Eugene W. |editor-last4=Clesceri |editor-first4=Lenore S. |editor-last5=Franson |editor-first5=Mary Ann H. |year=2005 |publisher=American Public Health Association |isbn=978-0-87553-047-5 |id=Also available on CD-ROM and [http://www.standardmethods.org/ online] by subscription}}</ref>

Common physical tests of water include temperature, Specific conductance or [[Physics:Electrical conductance|electrical conductance]] (EC) or conductivity, solids concentrations (e.g., [[Earth:Total suspended solids|total suspended solids]] (TSS)) and [[Biology:Turbidity|turbidity]]. Water samples may be examined using [[Chemistry:Analytical chemistry|analytical chemistry]] methods. Many published test methods are available for both organic and inorganic compounds. Frequently used parameters that are quantified are [[Chemistry:PH|pH]], BOD,<ref name="Newton">{{cite book |vauthors=Newton D |title=Chemistry of the Environment |publisher=Checkmark Books |year=2008 |isbn=978-0-8160-7747-2}}</ref>{{rp|102}} [[Biology:Chemical oxygen demand|chemical oxygen demand]] (COD),<ref name="Newton" />{{rp|104}} dissolved oxygen (DO), [[Physics:Hard water|total hardness]], nutrients ([[Chemistry:Nitrogen|nitrogen]] and [[Chemistry:Phosphorus|phosphorus]] compounds, e.g. [[Chemistry:Nitrate|nitrate]] and orthophosphates), metals (including copper, [[Chemistry:Zinc|zinc]], [[Chemistry:Cadmium|cadmium]], lead and [[Chemistry:Mercury (element)|mercury]]), oil and grease, total [[Chemistry:Petroleum|petroleum]] hydrocarbons (TPH), [[Biology:Surfactant|surfactant]]s and [[Biology:Pesticide|pesticide]]s.

The use of a biomonitor or [[Earth:Bioindicator|bioindicator]] is described as [[Chemistry:Biomonitoring|biological monitoring]]. This refers to the measurement of specific properties of an organism to obtain information on the surrounding physical and chemical environment.<ref name=":22">{{Cite report |date=March 2016 |title=National Rivers and Streams Assessment 2008–2009: A Collaborative Study |url=https://www.epa.gov/sites/production/files/2016-03/documents/nrsa_0809_march_2_final.pdf |publisher=EPA |id=EPA 841/R-16/007}}</ref> Biological testing involves the use of plant, animal or microbial indicators to monitor the health of an [[Earth:Aquatic ecosystem|aquatic ecosystem]]. They are any biological species or group of species whose function, population, or status can reveal what degree of ecosystem or environmental integrity is present.<ref name="Karr">{{cite journal |vauthors=Karr JR |year=1981 |title=Assessment of biotic integrity using fish communities |journal=Fisheries |volume=6 |issue=6 |pages=21–27 |doi=10.1577/1548-8446(1981)006<0021:AOBIUF>2.0.CO;2 |issn=1548-8446}}</ref> One example of a group of bio-indicators are the [[Biology:Copepod|copepod]]s and other small water [[Biology:Crustacean|crustacean]]s that are present in many water bodies. Such organisms can be monitored for changes (biochemical, physiological, or behavioral) that may indicate a problem within their ecosystem.

{{excerpt|Water quality#Sample collection|section=Sample collection|paragraphs=1|file=no}}

== Impacts ==
[[File:Fish Kill 745F2A9C-65B8-D693-7ABA3282F6A1ECE4.jpg|thumb|right|Oxygen depletion, resulting from nitrogen pollution and eutrophication, is a common cause of fish kills.]]

=== Ecosystems ===
Water pollution is a major global environmental problem because it can result in the degradation of all [[Earth:Aquatic ecosystem|aquatic ecosystem]]s – fresh, coastal, and ocean waters.<ref name="HäderHelblingVillafañe2021">{{cite book |author1=Donat-P. Häder |author2=E. Walter Helbling |author3=Virginia E. Villafañe |date=30 September 2021 |title=Anthropogenic Pollution of Aquatic Ecosystems |publisher=Springer Nature |isbn=978-3-030-75602-4 |url=https://books.google.com/books?id=ZtxFEAAAQBAJ |access-date=9 August 2022 |page=1 |quote=Pollution is a major stress factor affecting all aquatic ecosystems including fresh, coastal and open ocean waters.}}</ref> The specific contaminants leading to pollution in water include a wide spectrum of chemicals, pathogens, and physical changes such as elevated temperature. While many of the chemicals and substances that are regulated may be naturally occurring ([[Chemistry:Calcium|calcium]], [[Chemistry:Sodium|sodium]], iron, [[Chemistry:Manganese|manganese]], etc.) the [[Chemistry:Concentration|concentration]] usually determines what is a natural component of water and what is a contaminant. High concentrations of naturally occurring substances can have negative impacts on aquatic flora and fauna. Oxygen-depleting substances may be natural materials such as plant matter (e.g. leaves and grass) as well as human-made chemicals. Other natural and anthropogenic substances may cause turbidity (cloudiness) which blocks light and disrupts plant growth, and clogs the [[Biology:Gill|gill]]s of some fish species.<ref name="Davies-ColleySmith2001">{{cite journal |last1=Davies-Colley |first1=R. J. |last2=Smith |first2=D. G. |title=Turbidity, Suspended Sediment and Water Clarity: A Review |journal=Journal of the American Water Resources Association |date=October 2001 |volume=37 |issue=5 |pages=1085–1101 |issn=1093-474X |eissn=1752-1688 |doi=10.1111/j.1752-1688.2001.tb03624.x |bibcode=2001JAWRA..37.1085D |s2cid=129093839 |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1752-1688.2001.tb03624.x |access-date=9 August 2022}}</ref>[[File:Dumping of faecal sludge into the river.jpg|thumb|[[Engineering:Septage|Fecal sludge]] collected from pit latrines is dumped into a river at the Korogocho slum in Nairobi, Kenya.]]

=== Public health and waterborne diseases ===
A study published in 2017 stated that "polluted water spread gastrointestinal diseases and [[Medicine:Parasitic disease|parasitic infections]] and killed 1.8&nbsp;million people" (these are also referred to as waterborne diseases).<ref>{{cite news |vauthors=Kelland K |date=2017-10-19 |title=Study links pollution to millions of deaths worldwide |publisher=Reuters |url=https://www.reuters.com/article/us-health-pollution/study-links-pollution-to-millions-of-deaths-worldwide-idUSKBN1CO39B}}</ref> Persistent exposure to pollutants through water are [[Earth:Environmental health|environmental health]] hazards, which can increase the likelihood for one to develop cancer or other diseases.<ref>Dovjak, Mateja; Kukec, Andreja (2019), "Health Outcomes Related to Built Environments", ''Creating Healthy and Sustainable Buildings'', Cham: Springer International Publishing, pp. 43–82, {{doi|10.1007/978-3-030-19412-3_2}}, {{ISBN|978-3-030-19411-6}}, {{S2CID|190160283}}</ref>

=== Eutrophication from nitrogen pollution ===
Nitrogen pollution can cause eutrophication, especially in lakes. Eutrophication is an increase in the concentration of chemical nutrients in an [[Earth:Ecosystem|ecosystem]] to an extent that increases the [[Earth:Primary production|primary productivity]] of the ecosystem. Subsequent negative environmental effects such as [[Earth:Anoxic waters|anoxia]] (oxygen depletion) and severe reductions in water quality may occur.<ref name="Von Sperling" />{{rp|131}} This can harm fish and other animal populations.

{{excerpt|eutrophication|paragraphs=1|file=no}}

=== Ocean acidification ===
[[Biology:Ocean acidification|Ocean acidification]] is another impact of water pollution. Ocean acidification is the ongoing decrease in the pH value of the Earth's oceans, caused by the uptake of [[Chemistry:Carbon dioxide|carbon dioxide]] ({{CO2}}) from the atmosphere.<ref name="cald03">{{cite journal |vauthors=Caldeira K, Wickett ME |title=Oceanography: anthropogenic carbon and ocean pH |journal=Nature |volume=425 |issue=6956 |pages=365 |date=September 2003 |pmid=14508477 |doi=10.1038/425365a |bibcode=2001AGUFMOS11C0385C |s2cid=4417880 |url=https://zenodo.org/record/1233227|doi-access=free }}</ref>

== Prevalence ==
Water pollution is a problem in [[Finance:Developing country|developing countries]] as well as in developed countries.

=== By country ===
For example, water pollution in India and China is widespread. About 90 percent of the water in the cities of China is polluted.<ref>{{cite news |url=http://www.chinadaily.com.cn/english/doc/2005-06/07/content_449451.htm |title=China says water pollution so severe that cities could lack safe supplies |work=China Daily |date=June 7, 2005}}</ref>{{world topic|Water pollution in|title=Water pollution by country|noredlinks=yes|state=expand}}

==Control and reduction==
[[File:Secondary treatment reactors - Blue Plains WWTP - 2016b.jpg|thumb|View of secondary treatment reactors (activated sludge process) at the Blue Plains Advanced Wastewater Treatment Plant, Washington, D.C., United States. Seen in the distance are the sludge digester building and thermal hydrolysis reactors.]]

=== Pollution control philosophy ===
One aspect of environmental protection are mandatory regulations but they are only part of the solution. Other important tools in pollution control include environmental education, economic instruments, market forces and stricter enforcements. Standards can be "precise" (for a defined quantifiable minimum or maximum value for a pollutant), or "imprecise" which would require the use of [[Engineering:Best available technology|Best available technology]] (BAT) or Best practicable environmental option (BPEO). Market-based economic instruments for pollution control can include: charges, subsidies, deposit or refund schemes, the creation of a market in pollution credits, and enforcement incentives.<ref name="Jones OA et al">{{Cite book |vauthors=Jones OA, Gomes RL |editor-first1=R. M. |editor-last1=Harrison |url=https://pubs.rsc.org/en/content/ebook/978-1-84973-648-0|title=Pollution: Causes, Effects and Control|publisher=Royal Society of Chemistry |year=2013 |isbn=978-1-84973-648-0 |edition=5th|chapter=Chapter 1: Chemical Pollution of the Aquatic Environment by Priority Pollutants and its Control|doi=10.1039/9781782626527 }}</ref>

Moving towards a holistic approach in chemical pollution control combines the following approaches: Integrated control measures, trans-boundary considerations, complementary and supplementary control measures, life-cycle considerations, the impacts of chemical mixtures.<ref name="Jones OA et al"/>

Control of water pollution requires appropriate [[Physics:Infrastructure|infrastructure]] and management plans. The infrastructure may include wastewater treatment plants, for example sewage treatment plants and [[Earth:Industrial wastewater treatment|industrial wastewater]] treatment plants. [[Earth:Agricultural wastewater treatment|Agricultural wastewater treatment]] for farms, and [[Earth:Erosion control|erosion control]] at construction sites can also help prevent water pollution. Effective control of urban runoff includes reducing speed and quantity of flow.

Water pollution requires ongoing evaluation and revision of [[Earth:Water resource policy|water resource policy]] at all levels (international down to individual aquifers and wells).

=== Sanitation and sewage treatment ===
{{Further|Engineering:Sanitation|Engineering:WASH|Chemistry:Water issues in developing countries}}
[[File:Drainage in Ghana 4.jpg|thumb|Plastic waste on the big drainage, and air pollution in the far end of the drainage in Ghana]]
Municipal wastewater can be treated by centralized sewage treatment plants, [[Earth:Decentralized wastewater system|decentralized wastewater system]]s, [[Earth:Nature-based solutions|nature-based solutions]]<ref name=":2">UN-Water (2018) [http://www.unwater.org/publications/world-water-development-report-2018/ World Water Development Report 2018: Nature-based Solutions for Water], Geneva, Switzerland</ref> or in [[Earth:Onsite sewage facility|onsite sewage facilities]] and septic tanks. For example, [[Chemistry:Waste stabilization pond|waste stabilization pond]]s are a low cost treatment option for sewage, particularly for regions with warm climates.<ref name="Von Sperling">{{Cite journal |last=Von Sperling |first=Marcos |date=2007 |title=Wastewater Characteristics, Treatment and Disposal |url=https://www.iwapublishing.com/books/9781843391616/wastewater-characteristics-treatment-and-disposal |journal=IWA Publishing |volume=6 |doi=10.2166/9781780402086 |isbn=978-1-78040-208-6 |doi-access=free}} [[File:CC-BY_icon.svg|50x50px]] Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License</ref>{{rp|182}} UV light (sunlight) can be used to degrade some pollutants in waste stabilization ponds (sewage lagoons).<ref>{{cite journal |vauthors=Wang Y, Fan L, Jones OA, Roddick F |title=Quantification of seasonal photo-induced formation of reactive intermediates in a municipal sewage lagoon upon sunlight exposure |journal=The Science of the Total Environment |volume=765 |pages=142733 |date=April 2021 |pmid=33572041 |doi=10.1016/j.scitotenv.2020.142733 |s2cid=225156609 |bibcode=2021ScTEn.765n2733W}}</ref> The use of safely managed sanitation services would prevent water pollution caused by lack of access to sanitation.<ref name="JMP2017" />

Well-designed and operated systems (i.e., with secondary treatment stages or more advanced tertiary treatment) can remove 90 percent or more of the pollutant load in sewage.<ref>{{cite report |title=Primer for Municipal Wastewater Treatment Systems |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=20017KBE.txt |date=2004 |publisher=EPA |page=11 |id=EPA 832-R-04-001}}</ref> Some plants have additional systems to remove [[Earth:Nutrient|nutrient]]s and pathogens. While such advanced treatment techniques will undoubtedly reduce the discharges of micropollutants, they can also result in large financial costs, as well as environmentally undesirable increases in energy consumption and [[Earth:Greenhouse gas emissions|greenhouse gas emissions]].<ref>{{cite journal |vauthors=Jones OA, Green PG, Voulvoulis N, Lester JN |title=Questioning the excessive use of advanced treatment to remove organic micropollutants from wastewater |journal=Environmental Science & Technology |volume=41 |issue=14 |pages=5085–5089 |date=July 2007 |pmid=17711227 |doi=10.1021/es0628248 |bibcode=2007EnST...41.5085J}}</ref> 

[[Earth:Sanitary sewer overflow|Sewer overflows]] during storm events can be addressed by timely maintenance and upgrades of the [[Engineering:Sewerage|sewerage system]]. In the US, cities with large combined systems have not pursued system-wide separation projects due to the high cost,<ref>{{cite web |vauthors=Renn AM |title=Wasted: How to Fix America's Sewers |url=https://media4.manhattan-institute.org/sites/default/files/R-AR-0216.pdf |date=2016-02-25 |page=7 |publisher=Manhattan Institute |location=New York, NY}}</ref> but have implemented partial separation projects and [[Earth:Green infrastructure|green infrastructure]] approaches.<ref>{{cite report |title=Greening CSO Plans: Planning and Modeling Green Infrastructure for Combined Sewer Overflow Control |url=https://www.epa.gov/sites/production/files/2015-10/documents/greening_cso_plans_0.pdf |date=March 2014 |publisher=EPA |id=832-R-14-001}}</ref> In some cases municipalities have installed additional CSO storage facilities<ref>{{cite web |url=https://www.dcwater.com/clean-rivers-project |title=Clean Rivers Project |author=<!--Not stated--> |publisher=District of Columbia Water and Sewer Authority |access-date=2021-09-21}}</ref> or expanded sewage treatment capacity.<ref>{{cite web |title=United States and Ohio Reach Clean Water Act Settlement with City of Toledo, Ohio |url=http://yosemite.epa.gov/opa/admpress.nsf/b1ab9f485b098972852562e7004dc686/59f70abeaacc274885256c24005e6240?OpenDocument |date=2002-08-28 |publisher=EPA |archive-url=https://web.archive.org/web/20160113095352/http://yosemite.epa.gov/opa/admpress.nsf/b1ab9f485b098972852562e7004dc686/59f70abeaacc274885256c24005e6240?OpenDocument |archive-date=2016-01-13 |id=Press release.}}
</ref>

===Industrial wastewater treatment===
{{excerpt|Industrial wastewater treatment|paragraphs=1|file=no}}

===Agricultural wastewater treatment{{anchor|Agricultural wastewater}}===
{{excerpt|Agricultural wastewater treatment|paragraphs=1|file=no}}

===Management of erosion and sediment control===
[[File:Silt fence EPA.jpg|right|thumb|[[Earth:Silt fence|Silt fence]] installed on a construction site]]
Sediment from construction sites can be managed by installation of [[Earth:Erosion control|erosion control]]s, such as mulching and [[Earth:Hydroseeding|hydroseeding]], and [[Earth:Sediment control|sediment control]]s, such as [[Earth:Sediment basin|sediment basin]]s and [[Earth:Silt fence|silt fence]]s.<ref>Tennessee Department of Environment and Conservation. Nashville, TN (2012). [http://tnepsc.org/handbook.asp "Tennessee Erosion and Sediment Control Handbook."]</ref> Discharge of toxic chemicals such as motor fuels and concrete washout can be prevented by use of spill prevention and control plans, and specially designed containers (e.g. for concrete washout) and structures such as overflow controls and diversion berms.<ref>{{cite report |date=February 2012 |title=Concrete Washout |series=Stormwater Best Management Practice |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100E60V.txt |publisher=EPA |id=BMP fact sheet. EPA 833-F-11-006}}</ref>

Erosion caused by deforestation and changes in [[Earth:Hydrology|hydrology]] (soil loss due to water runoff) also results in loss of sediment and, potentially, water pollution.<ref>{{cite journal |vauthors = Mapulanga AM, Naito H |title=Effect of deforestation on access to clean drinking water |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=116 |issue=17 |pages=8249–8254 |date=April 2019 |pmid=30910966 |pmc=6486726 |doi=10.1073/pnas.1814970116 |doi-access=free |bibcode=2019PNAS..116.8249M}}</ref><ref>{{Cite web |author=University of Basel |title=Climate change and land use are accelerating soil erosion by water |url=https://www.sciencedaily.com/releases/2020/08/200824165633.htm |date=2020-08-24 |website=Science Daily}}</ref>

=== Control of urban runoff (storm water) ===
{{excerpt|Urban runoff#Prevention and mitigation|paragraphs=1,2|file=no}}
{{clear right}}[[File:Water-bodies-good-water-quality.svg|thumb|Share of water bodies with good [[Earth:Water quality|water quality]] in 2020. A water body is classified as "good" quality if at least 80% of monitoring values meet target quality levels, see also SDG 6, Indicator 6.3.2.]]

=== Legislation ===
==== Philippines ====
In the Philippines, Republic Act 9275, otherwise known as the Philippine Clean Water Act of 2004,<ref name="LawPhil2004">{{Cite web |title=An Act Providing for a Comprehensive Water Quality Management And For Other Purposes |url=http://www.lawphil.net/statutes/repacts/ra2004/ra_9275_2004.html |url-status=live |archive-url=https://web.archive.org/web/20160921041418/http://www.lawphil.net/statutes/repacts/ra2004/ra_9275_2004.html|archive-date=21 September 2016 |access-date=September 30, 2016 |website=The LawPhil Project |df=dmy-all}}</ref> is the governing law on wastewater management. It states that it is the country's policy to protect, preserve and revive the quality of its fresh, brackish and marine waters, for which wastewater management plays a particular role.<ref name="LawPhil2004" />

==== United States ====
{{excerpt|Water pollution in the United States#Current regulations|paragraphs=1|file=no}}

== See also ==
* [[Earth:Aquatic toxicology|Aquatic toxicology]]
* {{sectionlink|Environmental impact of pesticides|Water}}
* Human impacts on the environment
* Pollution
* [[Earth:Trophic state index|Trophic state index]] (water quality indicator for lakes)
* [[Earth:VOC contamination of groundwater|VOC contamination of groundwater]]
* [[Earth:Water resource management|Water resources management]]
* [[Earth:Water security|Water security]]

== References ==
{{Reflist}}

== External links ==
{{commons}}
{{Library resources box |by=no |onlinebooks=no |others=yes lcheading=Water – Pollution}}
* [https://www.unep.org/explore-topics/water/what-we-do/tackling-global-water-pollution Tackling global water pollution] – UN Environment Programme

{{pollution}}
{{marine pollution}}
{{water}}
{{Natural resources}}
{{Environmental science}}


{{DEFAULTSORT:Water Pollution}}
[[Category:Water pollution| ]]
[[Category:Aquatic ecology]]
[[Category:Environmental science]]
[[Category:Water and the environment]]

{{Sourceattribution|Water pollution}}