Water pollution#Chemical testing

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."{{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.

{{Further|Waterborne diseases#Diseases by type of pathogen|Sewage#Pathogens}}

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.
• Disinfection by-products found in chemically disinfected drinking water (whilst these chemicals can be a pollutant in the water distribution network, they are fairly volatile and therefore not usually found in environmental waters).{{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}}
• Hormones (from animal husbandry and residue from human hormonal contraception methods) and synthetic materials such as phthalates 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.{{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}}[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.{{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}}
• Insecticides and herbicides, often from agricultural runoff.
• Pathogens like Hepatovirus A (HAV may be present in treated wastewater outflows and receiving water bodies but is largely removed during further treatment of drinking water{{cite journal|vauthors=Takuissu GR, Kenmoe S, Ebogo-Belobo JT, Kengne-Ndé C, Mbaga DS, Bowo-Ngandji A, Ondigui JL, Kenfack-Momo R, Tcatchouang S, Kenfack-Zanguim J, Fogang RL, Menekem EZ, Kame-Ngasse GI, Magoudjou-Pekam JN, Veneri C, Mancini P, Ferraro GB, Iaconelli M, Orlandi L, Del Giudice C, Suffredini E, La Rosa G|display-authors=6|title=Occurrence of Hepatitis A Virus in Water Matrices: A Systematic Review and Meta-Analysis|year=2023|journal=International Journal of Environmental Research and Public Health|volume=20|issue=2|page=1054|id=Art. No. 1054|doi=10.3390/ijerph20021054|doi-access=free|pmid=36673812|pmc=9859052}})

Inadequately treated wastewater can convey nutrients, pathogens, heterogenous suspended solids and organic fecal matter.{{rp|6}}

File:South Asia Poster 03.jpg

Bacteria, viruses, protozoans and parasitic worms are examples of pathogens that can be found in wastewater.{{rp|47}} In practice, indicator organisms 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 (bacterial indicator) of fecal contamination of water samples most commonly used are total coliforms (TC) or fecal coliforms (FC), the latter also referred to as thermotolerant coliforms, such as Escherichia coli.{{rp|52–53}}

Pathogens can produce waterborne diseases in either human or animal hosts.{{Cite book |url=https://pubs.rsc.org/en/content/ebook/978-1-84973-648-0 |title=Pollution: Causes, effects, and control |date=2013 |publisher=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}} Some microorganisms sometimes found in contaminated surface waters that have caused human health problems include Burkholderia pseudomallei, Cryptosporidium parvum, Giardia lamblia, Salmonella, norovirus and other viruses, and parasitic worms including the Schistosoma type.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.

The source of high levels of pathogens in water bodies can be from human feces (due to open defecation), sewage, blackwater, or 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 sanitation systems (septic tanks, pit latrines), sewage treatment plants without disinfection steps, sanitary sewer overflows and combined sewer overflows (CSOs){{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}} during storm events and intensive agriculture (poorly managed livestock operations).

Organic substances that enter water bodies are often toxic.{{cite book |vauthors=Laws EA |url=https://books.google.com/books?id=V5D2DQAAQBAJ |title=Aquatic Pollution: An Introductory Text |date=2018 |publisher=John Wiley & Sons |isbn=978-1-119-30450-0 |edition=4th |location=Hoboken, NJ |via=Google Books}}{{rp|229}}

• Petroleum hydrocarbons, including fuels (gasoline, diesel fuel, jet fuels, and fuel oil) and lubricants (motor oil), and fuel combustion byproducts, from oil spills or storm water runoff{{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}}
• Volatile organic compounds, such as improperly stored industrial solvents. Problematic species are organochlorides such as polychlorinated biphenyl (PCBs) and trichloroethylene, a common solvent.

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants.{{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=Environmental Toxicology and Chemistry |volume=40 |issue=3 |pages=543–549 |date=March 2021 |pmid=32452041 |pmc=8387100 |doi=10.1002/etc.4784}}{{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.25827340S}}

File:Bützflethermoor Rotschlammdeponie Luftaufnahmen 2012-05-by-RaBoe-478-1.jpg 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

Inorganic water pollutants include:

• Ammonia from food processing waste
• Heavy metals from motor vehicles (via urban storm water runoff)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. and acid mine drainage
• Nitrates and phosphates, from sewage and agriculture (see nutrient pollution)
• Silt (sediment) in runoff from construction sites or sewage, logging, slash and burn practices land clearing sites
• Salt: Freshwater salinization is the process of salty runoff contaminating freshwater ecosystems.{{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}} Human-induced salinization is termed as secondary salinization, with the use of de-icing road salts as the most common form of runoff.{{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}}{{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}}

{{excerpt|Environmental impact of pharmaceuticals and personal care products|paragraphs=1-3|file=no}}

• Environmental persistent pharmaceutical pollutants, which can include various pharmaceutical drugs and their metabolites (see also drug pollution), such as antidepressant drugs, antibiotics or the contraceptive pill.
• Metabolites of illicit drugs (see also wastewater epidemiology), for example methamphetamine and ecstasy.{{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}}{{Cite web |last=De Lorenzo |first=D |title=MDMA Gangs Are Literally Polluting Europe |url=https://www.vice.com/en/article/mdma-gangs-are-literally-polluting-europe/ |date=2021-06-18 |website=Vice World News |publisher=Vice Media Group |location=Brooklyn, NY}}

File:Canal-pollution.jpg, Canada]]

{{Further|Sewage#Solid waste|Plastic pollution|Marine plastic pollution}}

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 macroscopic pollution– large visible items polluting the water– but also microplastics pollution that is not directly visible. The terms marine debris and marine plastic pollution are used in the context of pollution of oceans.

Microplastics persist in the environment at high levels, particularly in aquatic and marine ecosystems, where they cause water pollution.{{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}} 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.{{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}}

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.{{Cite web|author=((European Investment Bank))|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|access-date=2024-04-12}}{{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}}

Surface water pollution includes pollution of rivers, lakes and oceans. A subset of surface water pollution is marine pollution which affects the oceans. Nutrient pollution refers to contamination by excessive inputs of nutrients.

Globally, about 4.5 billion people do not have safely managed sanitation as of 2017, according to an estimate by the Joint Monitoring Programme for Water Supply and Sanitation.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 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 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, Europe and Central Asia account for around 16% of global microplastics discharge into the seas,{{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}} and although management of plastic waste and its recycling is improving globally, the absolute amount of plastic pollution continues to increase unabated due to the large amount of plastic that is being produced and disposed of.{{Cite journal|last1=Ritchie |first1=Hannah|author1-link=Hannah Ritchie |last2=Samborska|first2=Veronika|last3=Roser |first3=Max |author3-link=Max Roser |year=2023|title=Plastic Pollution |url=https://ourworldindata.org/plastic-pollution |journal=Our World in Data|access-date=12 April 2024}} Even if sea plastic pollution were to stop entirely, microplastic contamination of the surface ocean would be projected to continue to increase.

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

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

File:Brayton Point Power Station.JPG in Massachusetts discharged heated water to Mount Hope Bay until 2011.]]

{{excerpt|Thermal pollution|paragraphs=1|file=no}}

Elevated water temperatures decrease 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 biodiversity, and foster invasion by new thermophilic species.{{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}}{{rp|179}}{{rp|375}}

The introduction of aquatic invasive organisms is a form of water pollution as well. It causes biological pollution.{{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 }}

{{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.{{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 }}

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 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).United States. Clean Water Act (CWA), section 502(14), {{USC|33|1362}} (14). 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.U.S. CWA section 402(p), {{USC|33|1342(p)}}

Sewage typically consists of 99.9% water and 0.1% solids.{{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}} Sewage contributes many classes of nutrients that lead to Eutrophication. It is a major source of phosphate for example.{{cite book |title=Water Pollution Control |year=2014 |isbn=978-1-118-86383-1 |veditors=Nesaratnam ST |doi=10.1002/9781118863831}} Sewage is often contaminated with diverse compounds found in personal hygiene, cosmetics, pharmaceutical drugs (see also drug pollution), and their metabolites 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 sanitary sewer overflows or combined sewer overflows.File:AngleseyCopperStream.jpg on Anglesey]]

File:Perfluorooctanesulfonic acid.svg (PFOS) is a global pollutant that has been found in drinking water. It appears not to biodegrade.{{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}}]]{{Further|Industrial wastewater treatment}}

Industrial processes that use water also produce wastewater. This is called 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. Some industries discharge chemical wastes, including solvents and heavy metals (which are toxic) and other harmful pollutants.

{{Excerpt|Oil spill|paragraphs=1|file=no}}

{{Excerpt|Nonpoint source pollution|paragraphs=1|file=no}}

Agriculture is a major contributor to water pollution from nonpoint sources. The use of fertilizers as well as surface runoff from farm fields, pastures and feedlots leads to nutrient pollution.{{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}} In addition to plant-focused agriculture, fish-farming is also a source of pollution. Additionally, agricultural runoff often contains high levels of pesticides.

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.{{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}}

Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids.{{Cite web |date=2022-06-24 |title=What is Acid Rain? |url=https://www.epa.gov/acidrain/what-acid-rain |publisher=EPA}} 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 lightning strikes and sulphur dioxide is produced by volcanic eruptions.{{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}} Acid rain can have harmful effects on plants, aquatic ecosystems and infrastructure.{{Cite web |date=2022-04-24 |title=Effects of Acid Rain |url=https://www.epa.gov/acidrain/effects-acid-rain |publisher=EPA}}{{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}}

Carbon dioxide concentrations in the atmosphere have increased since the 1850s due anthropogenic influences (emissions of greenhouse gases). This leads to ocean acidification and is another form of water pollution from atmospheric contributions.{{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 }}

File:Research- water sampling equipment.jpg preparing water autosamplers]]

{{Further|Water quality#Sampling and measurement|Environmental monitoring|Analysis of water chemistry|Water sampling station|Regulation and monitoring of pollution#Water pollution}}

Water pollution may be analyzed through several broad categories of methods: physical, chemical and biological. Some methods may be conducted 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.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}}

Common physical tests of water include temperature, Specific conductance or electrical conductance (EC) or conductivity, solids concentrations (e.g., total suspended solids (TSS)) and turbidity. Water samples may be examined using analytical chemistry methods. Many published test methods are available for both organic and inorganic compounds. Frequently used parameters that are quantified are pH, BOD,{{cite book |vauthors=Newton D |title=Chemistry of the Environment |publisher=Checkmark Books |year=2008 |isbn=978-0-8160-7747-2}}{{rp|102}} chemical oxygen demand (COD),{{rp|104}} dissolved oxygen (DO), total hardness, nutrients (nitrogen and phosphorus compounds, e.g. nitrate and orthophosphates), metals (including copper, zinc, cadmium, lead and mercury), oil and grease, total petroleum hydrocarbons (TPH), surfactants and pesticides.

The use of a biomonitor or bioindicator is described as biological monitoring. This refers to the measurement of specific properties of an organism to obtain information on the surrounding physical and chemical environment.{{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}} Biological testing involves the use of plant, animal or microbial indicators to monitor the health of an 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.{{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 |bibcode=1981Fish....6f..21K |issn=1548-8446}} One example of a group of bio-indicators are the copepods and other small water crustaceans 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}}

File:Fish Kill 745F2A9C-65B8-D693-7ABA3282F6A1ECE4.jpg, resulting from nitrogen pollution and eutrophication, is a common cause of fish kills.]]

Water pollution is a major global environmental problem because it can result in the degradation of all aquatic ecosystems – fresh, coastal, and ocean waters.{{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.}} 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 (calcium, sodium, iron, manganese, etc.) the 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 gills of some fish species.{{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}}File:Dumping of faecal sludge into the river.jpg collected from pit latrines is dumped into a river at the Korogocho slum in Nairobi, Kenya.]]

{{Further|WASH#Health aspects}}

A study published in 2017 stated that "polluted water spread gastrointestinal diseases and parasitic infections and killed 1.8 million people" (these are also referred to as waterborne diseases).{{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}} Persistent exposure to pollutants through water are environmental health hazards, which can increase the likelihood for one to develop cancer or other diseases.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}}

Nitrogen pollution can cause eutrophication, especially in lakes. Eutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases the primary productivity of the ecosystem. Subsequent negative environmental effects such as anoxia (oxygen depletion) and severe reductions in water quality may occur.{{rp|131}} This can harm fish and other animal populations.

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

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 carbon dioxide ({{CO2}}) from the atmosphere.{{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 }}

Water pollution is a problem in developing countries as well as in developed countries.

For example, water pollution in India and China is widespread. About 90 percent of the water in the cities of China is polluted.{{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}}{{world topic|Water pollution in|title=Water pollution by country|noredlinks=yes|state=expand}}

File:Secondary treatment reactors - Blue Plains WWTP - 2016b.jpg, Washington, D.C., United States. Seen in the distance are the sludge digester building and thermal hydrolysis reactors.]]

One aspect of environmental protection is mandatory regulations, which are only part of the solution. Other important tools in pollution control include environmental education, economic instruments, market forces, and stricter enforcement. Standards can be "precise" (for a defined quantifiable minimum or maximum value for a pollutant), or "imprecise" which would require the use of 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.{{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 }}

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.

Control of water pollution requires appropriate infrastructure and management plans. The infrastructure may include wastewater treatment plants, for example sewage treatment plants and industrial wastewater treatment plants. Agricultural wastewater treatment for farms, and 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 water resource policy at all levels (international down to individual aquifers and wells).

{{Further|Sanitation|WASH|Water issues in developing countries}}

File:Drainage in Ghana 4.jpg

Municipal wastewater can be treated by centralized sewage treatment plants, decentralized wastewater systems, nature-based solutionsUN-Water (2018) [http://www.unwater.org/publications/world-water-development-report-2018/ World Water Development Report 2018: Nature-based Solutions for Water], Geneva, Switzerland or in onsite sewage facilities and septic tanks. For example, waste stabilization ponds can be a low cost treatment option for sewage.{{Cite journal|last=Von Sperling |first=Marcos |date=2007 |title=Wastewater Characteristics, Treatment and Disposal |journal=Water Intelligence Online |publisher=IWA Publishing|series=Biological Wastewater Treatment|volume=6 |doi=10.2166/9781780402086 |isbn=978-1-78040-208-6 |doi-access=free}}{{rp|182}} UV light (sunlight) can be used to degrade some pollutants in waste stabilization ponds (sewage lagoons).{{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.76542733W}} The use of safely managed sanitation services would prevent water pollution caused by lack of access to sanitation.

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.{{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}} Some plants have additional systems to remove nutrients 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 greenhouse gas emissions.{{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}}

Sewer overflows during storm events can be addressed by timely maintenance and upgrades of the sewerage system. In the US, cities with large combined systems have not pursued system-wide separation projects due to the high cost,{{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}} but have implemented partial separation projects and green infrastructure approaches.{{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}} In some cases municipalities have installed additional CSO storage facilities{{cite web |url=https://www.dcwater.com/cleanrivers |title=Clean Rivers Project |author= |publisher=District of Columbia Water and Sewer Authority |location=Washington, DC |access-date=2024-04-13}} or expanded sewage treatment capacity.{{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.}}

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

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

File:Silt fence EPA.jpg installed on a construction site]]

Sediment from construction sites can be managed by installation of erosion controls, such as mulching and hydroseeding, and sediment controls, such as sediment basins and silt fences.Tennessee Department of Environment and Conservation. Nashville, TN (2012). [http://tnepsc.org/handbook.asp "Tennessee Erosion and Sediment Control Handbook."] 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.{{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}}

Erosion caused by deforestation and changes in hydrology (soil loss due to water runoff) also results in loss of sediment and, potentially, water pollution.{{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}}{{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}}

{{excerpt|Urban runoff#Prevention and mitigation|paragraphs=1,2|file=no}}

{{clear right}}File:Water-bodies-good-water-quality.svg 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.]]

In the Philippines, Republic Act 9275, otherwise known as the Philippine Clean Water Act of 2004,{{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}} 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.

In 2024, The Royal Academy of Engineering released a study into the effects wastewater on public health in the United Kingdom.{{cite web |title=Testing the waters Priorities for mitigating health risks from wastewater pollution |url=https://nepc.raeng.org.uk/media/qi2eyivp/testing-the-waters-priorities-for-mitigating-health-risks-from-wastewater-pollution.pdf |publisher=Royal Academy of Engineering |date=May 2024}} The study gained media attention, with comments from the UKs leading health professionals, including Sir Chris Whitty. Outlining 15 recommendations for various UK bodies to dramatically reduce public health risks by increasing the water quality in its waterways, such as rivers and lakes.

After the release of the report, The Guardian newspaper interviewed Whitty, who stated that improving water quality and sewage treatment should be a high level of importance and a "public health priority". He compared it to eradicating cholera in the 19th century in the country following improvements to the sewage treatment network.{{cite web |title=Reducing sewage in rivers and seas is public health priority, says Chris Whitty |url=https://www.theguardian.com/society/article/2024/may/21/reducing-sewage-rivers-seas-public-health-priority-chris-whitty |publisher=The Guardian}} The study also identified that low water flows in rivers saw high concentration levels of sewage, as well as times of flooding or heavy rainfall. While heavy rainfall had always been associated with sewage overflows into streams and rivers, the British media went as far to warn parents of the dangers of paddling in shallow rivers during warm weather.{{cite web |last1=Blakely |first1=Rhys |title=Paddling in rivers this summer could make children ill, warns Whitty |url=https://www.thetimes.com/uk/environment/article/paddling-in-rivers-this-summer-could-make-children-ill-warns-whitty |publisher=The Times}}

Whitty's comments came after the study revealed that the UK was experiencing a growth in the number of people that were using coastal and inland waters recreationally. This could be connected to a growing interest in activities such as open water swimming or other water sports.{{cite web |last1=Speare-Cole |first1=Rebecca |title=Minimising sewage in UK waters is a ‘public health priority’ – Chris Whitty |url=https://www.independent.co.uk/climate-change/news/chris-whitty-people-devon-government-university-of-leeds-b2548414.html |publisher=The Independent}} Despite this growth in recreation, poor water quality meant some were becoming unwell during events.{{cite web |title=Dozens of triathletes left severely ill after swimming in River Thames |url=https://www.independent.co.uk/news/uk/home-news/thames-water-pollution-river-thames-triathlon-b2561829.html |publisher=The Independent}} Most notably, the 2024 Paris Olympics had to delay numerous swimming-focused events like the triathlon due to high levels of sewage in the River Seine.{{cite web |title=What's the problem with swimming in the Seine? |url=https://www.bbc.co.uk/news/articles/cn05d4k0l2qo#:~:text=It%20should%20be%20a%20stunning,be%20postponed%20for%20a%20day. |publisher=BBC}}

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

{{Portal|Water|Environment}}

• Aquatic toxicology
• {{section link|Environmental impact of pesticides|Water}}
• Human impacts on the environment
• Phytoremediation
• Pollution
• Trophic state index (water quality indicator for lakes)
• VOC contamination of groundwater
• Water resources management
• Water security

{{Reflist}}

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{{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

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