View source for Water quality

{{Short description|Assessment against standards for use}}
{{Use dmy dates|date=September 2020}}
[[File:Rosette sampler EPA.gif|thumb|right|A [[rosette sampler]] is used for collecting water samples in deep water, such as the [[Great Lakes]] or oceans, for water quality testing.]]

'''Water quality''' refers to the [[Chemical property|chemical]], [[Physical property|physical]], and [[Biology|biological]] characteristics of [[water]] based on the standards of its usage.<ref name="water quality">{{Cite web |last=Cordy|first=Gail E. |date=March 2001 |title=A Primer on Water Quality |url=https://pubs.usgs.gov/fs/fs-027-01/ |publisher=U.S. Geological Survey (USGS) |location=Reston, VA |id=FS-027-01}}</ref><ref>{{cite journal |first1=D. L. |last1=Johnson |first2=S. H. |last2=Ambrose |first3=T. J. |last3=Bassett |first4=M. L.|last4=Bowen|title=Meanings of Environmental Terms|journal=Journal of Environmental Quality |pages=581–589 |volume=26 |issue=3 |doi=10.2134/jeq1997.00472425002600030002x |first5=D. E.|last5=Crummey |first6=J. S. |last6=Isaacson |first7=D. N. |last7=Johnson |first8=P. |last8=Lamb |first9=M. |last9=Saul |first10=A. E. |last10=Winter-Nelson |year=1997|bibcode=1997JEnvQ..26..581J }}</ref> It is most frequently used by reference to a set of standards against which compliance, generally achieved through [[Water treatment|treatment]] of the water, can be assessed. The most common standards used to monitor and assess water quality convey the health of [[ecosystems]], [[safety]] of human contact, extent of [[water pollution]] and condition of [[drinking water]]. Water quality has a significant impact on [[water supply]] and often determines supply options.<ref name="WHO DW quality">{{cite report |title=Guidelines for Drinking-water Quality: Fourth edition incorporating the first addendum |url=https://apps.who.int/iris/handle/10665/254637 |date=2017 |publisher=World Health Organization (WHO) |location=Geneva |hdl=10665/254637 |isbn=9789241549950}}</ref>

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== Impacts on public health ==
{{See also|Drinking water#Quality}}
Over time, there has been increasing recognition of the importance of [[Drinking water quality standards|drinking water quality]] and its impact on [[public health]]. This has led to increasing protection and management of water quality.<ref name=":0">{{Cite journal |last1=Khan |first1=Nameerah |last2=Charles |first2=Katrina J. |date=2023 |title=When Water Quality Crises Drive Change: A Comparative Analysis of the Policy Processes Behind Major Water Contamination Events |journal=Exposure and Health |language=en |volume=15 |issue=3 |pages=519–537 |doi=10.1007/s12403-022-00505-0 |issn=2451-9766 |pmc=9522453 |pmid=36196073 |doi-access=free|bibcode=2023ExpHe..15..519K }} [[File:CC-BY_icon.svg|50x50px]] Text was copied from this source, which is available under a [[creativecommons:by/4.0/|Creative Commons Attribution 4.0 International License]]</ref>

The understanding of the links between water quality and health continues to grow and highlight new potential health crises: from the chronic impacts of [[infectious diseases]] on child development through [[Stunted growth|stunting]] to new evidence on the harms from known contaminants, such as [[manganese]] with growing evidence of [[neurotoxicity]] in children.<ref name=":0" /> In addition, there are many emerging water quality issues—such as [[microplastics]], [[Perfluorinated compound|perfluorinated compounds]], and [[antimicrobial resistance]].<ref name=":0" />

== Categories ==
The parameters for water quality are determined by the intended use. Work in the area of water quality tends to be focused on water that is [[Water treatment|treated]] for potability, industrial/domestic use, or [[Restoration ecology|restoration]] (of an environment/ecosystem, generally for health of human/aquatic life).<ref>{{Cite web |date=2021-08-10 |title=Other Uses and Types of Water |url=https://www.cdc.gov/healthywater/other/index.html |publisher=US Centers for Disease Control and Prevention (CDC) |location=Atlanta, GA}}</ref>

===Human consumption===
[[File:Chemical contamination of drinking water.jpg|upright=1.4|thumb|Regional and national contamination of drinking water by chemical type and population size at risk of exposure]]
Contaminants that may be in untreated water include [[microorganism]]s such as [[virus]]es, [[protozoa]] and [[bacteria]]; [[Inorganic compound|inorganic]] contaminants such as [[Salt (chemistry)|salts]] and [[metals]]; [[Organic compound|organic chemical]] contaminants from industrial processes and [[petroleum]] use; [[pesticides]] and [[herbicides]]; and [[radioactive]] contaminants. Water quality depends on the local [[geology]] and [[ecosystem]], as well as human uses such as sewage dispersion, industrial pollution, use of water bodies as a [[heat sink]], and overuse (which may lower the level of the water).{{Citation needed|date=October 2022}}

The [[United States Environmental Protection Agency]] (EPA) limits the amounts of certain contaminants in [[tap water]] provided by US [[public water system]]s. The [[Safe Drinking Water Act]] authorizes EPA to issue two types of standards:
* ''primary standards'' regulate substances that potentially affect human health;<ref>U.S. Environmental Protection Agency (EPA), Washington, D.C. "National Primary Drinking Water Regulations." ''Code of Federal Regulations,'' {{uscfr|40|141}}.</ref><ref name="EPA DW reqts">{{cite web |url=https://www.epa.gov/dwreginfo/drinking-water-regulations |title=Drinking Water Regulations |author=<!--Not stated--> |date=2024-12-10 |website=Drinking Water Requirements for States and Public Water Systems |publisher=EPA}}</ref>
* ''secondary standards'' prescribe aesthetic qualities, those that affect taste, odor, or appearance.<ref>{{cite web |url=https://www.epa.gov/sdwa/secondary-drinking-water-standards-guidance-nuisance-chemicals |title=Secondary Drinking Water Standards: Guidance for Nuisance Chemicals |author=<!--Not stated--> |date=2025-06-02 |publisher=EPA}}</ref>

The U.S. [[Food and Drug Administration]] (FDA) regulations establish limits for contaminants in [[bottled water]].<!--{{fv}}: must provide the same protection for public health.--><ref>{{cite web |url=https://www.fda.gov/Food/FoodborneIllnessContaminants/BuyStoreServeSafeFood/ucm046894.htm |archive-url=https://web.archive.org/web/20130414233847/http://www.fda.gov/Food/FoodborneIllnessContaminants/BuyStoreServeSafeFood/ucm046894.htm |url-status=dead |archive-date=14 April 2013 |title=FDA Regulates the Safety of Bottled Water Beverages Including Flavored Water and Nutrient-Added Water Beverages |author=<!--Not stated--> |date=2018-09-22 |website=Food Facts for Consumers |publisher=U.S. Food and Drug Administration |location=Silver Spring, MD}}</ref> Drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants. The presence of these contaminants does not necessarily indicate that the water poses a health risk.

In [[urbanization|urbanized]] areas around the world, [[water purification]] technology is used in municipal water systems to remove contaminants from the source water (surface water or [[groundwater]]) before it is distributed to homes, businesses, schools and other recipients. Water drawn directly from a stream, lake, or [[aquifer]] and that has no treatment will be of uncertain quality in terms of potability.<ref name="WHO DW quality"/>

The burden of polluted drinking water disproportionally effects under-represented and vulnerable populations.<ref>{{cite book |last1=Katner |first1=A. L. |last2=Brown |first2=K |last3=Pieper |first3=K. |last4=Edwards |first4=M |last5=Lambrinidou |first5=Y |last6=Subra |first6=W. |editor-last1=Brinkmann |editor-first1=R. |editor-last2=Garren |editor-first2=S. |date=2018 |chapter=America’s Path to Drinking Water Infrastructure Inequality and Environmental Injustice: The Case of Flint, Michigan |title=The Palgrave Handbook of Sustainability |publisher=Palgrave Macmillan |location=London |pages=79–97 |doi=10.1007/978-3-319-71389-2_5|isbn=978-3-319-71388-5 }}</ref> Communities that lack these clean drinking-water services are at risk of contracting water-borne and pollution-related illnesses like Cholera, [[diarrhea]], dysentery, hepatitis A, typhoid, and polio.<ref>{{cite web |title=Drinking-water |url=https://www.who.int/en/news-room/fact-sheets/detail/drinking-water |date=2022-03-21 |publisher=WHO |id=Fact sheet}}</ref> These communities are often in low-income areas, where human wastewater is discharged into a nearby drainage channel or surface water drain without sufficient treatment, or is used in agricultural irrigation.

===Industrial and domestic use===
[[Solvation|Dissolved]] [[ions]] may affect the suitability of water for a range of industrial and domestic purposes. The most familiar of these is probably the presence of [[calcium]] (Ca<sup>2+</sup>) and [[magnesium]] (Mg<sup>2+</sup>) that interfere with the cleaning action of [[soap]], and can form hard [[sulfate]] and soft [[carbonate]] [[Precipitation|deposits]] in water [[heater]]s or [[boiler]]s.<ref>{{cite book |last1=Babbitt |first1=Harold E. |last2=Doland |first2=James J. |title=Water Supply Engineering |date=1949 |publisher=McGraw-Hill |location=New York |asin=B000OORYE2 |page=388}}</ref> Hard water may be softened to remove these ions. The softening process often substitutes [[sodium]] cations.<ref>{{cite book |last1=Linsley |first1=Ray K |last2=Franzini |first2=Joseph B. |title=Water-Resources Engineering |date=1972 |publisher=McGraw-Hill |isbn=0-07-037959-9 |pages=454–456}}</ref> For certain populations, hard water may be preferable to soft water because health problems have been associated with calcium deficiencies and with excess sodium.<ref>WHO (2004). [https://www.who.int/entity/water_sanitation_health/dwq/nutrconsensusrep.pdf "Consensus of the Meeting: Nutrient minerals in drinking-water and the potential health consequences of long-term consumption of demineralized and remineralized and altered mineral content drinking-waters."] ''Rolling Revision of the WHO Guidelines for Drinking-Water Quality (draft).'' From 11–13 November 2003 meeting in Rome, Italy at the WHO European Centre for Environment and Health.</ref> The necessity for additional calcium and magnesium in water depends on the population in question because people generally satisfy their recommended amounts through food.<ref name="WHO DW quality"/>{{rp|99, 115, 377}}

===Environmental water quality===
{{multiple image
| total_width       = 400
| image1            = Water cleanliness sign, Dublin.jpg
| caption1          = Sign in [[Sandymount]], Ireland, describing water quality, giving levels of [[Fecal coliform|faecal coliform]] ''[[E. coli]]'' and ''[[Enterococcus faecalis]]''
| image2            = View of urban runoff discharging to coastal waters.jpg
| caption2          = [[Urban runoff]] discharging to coastal waters
}}
{{See also|Environmental monitoring|Freshwater environmental quality parameters}}

'''Environmental water quality''', also called '''ambient water quality,''' relates to water bodies such as [[lake]]s, [[river]]s, and [[ocean]]s.<ref>{{Cite web |url=https://www.epa.gov/wqs-tech/supplemental-module-human-health-ambient-water-quality-criteria |archive-url=https://web.archive.org/web/20151015033851/http://www2.epa.gov/wqs-tech/supplemental-module-human-health-ambient-water-quality-criteria |url-status=dead |archive-date=15 October 2015 |title=Supplemental Module: Human Health Ambient Water Quality Criteria |date=2022-06-28 |publisher=EPA}}</ref> Water quality standards for surface waters vary significantly due to different environmental conditions, ecosystems, and intended human uses. Toxic substances and high populations of certain [[microorganism]]s can present a health hazard<ref>{{Cite journal |last1=Adlish |first1=John I. |last2=Costa |first2=Davide |last3=Mainardi |first3=Enrico |last4=Neuhold |first4=Piero |last5=Surrente |first5=Riccardo |last6=Tagliapietra |first6=Luca J.|date=2020-10-31|title=Polyethylene Identification in Ocean Water Samples by Means of 50 keV Energy Electron Beam |journal=Instruments |volume=4 |issue=4 |pages=32 |doi=10.3390/instruments4040032 |arxiv=2009.03763 |quote=Plastic is the most common type of marine debris found in oceans, and it is the most widespread problem affecting the marine environment. It also threatens ocean health, food safety and quality, human health, and coastal tourism, and it contributes to climate change |doi-access=free}}</ref> for non-drinking purposes such as irrigation, swimming, fishing, rafting, boating, and industrial uses. These conditions may also affect wildlife, which use the water for drinking or as a habitat. According to the EPA, water quality laws generally specify protection of fisheries and recreational use and require, as a minimum, retention of current quality standards.<ref>{{Cite book |url=https://www.epa.gov/sites/default/files/2014-10/documents/handbook-chapter3.pdf |title=Water Quality Standards Handbook Chapter 3: Water Quality Criteria |publisher=EPA |year=2017 |id=EPA 823-B-17-001}}</ref> In some locations, desired water quality conditions include high [[Oxygen saturation|dissolved oxygen]] concentrations, low [[Chlorophyll a|chlorophyll-a]] concentrations, and high [[water clarity]].<ref name="Tango">{{cite journal | last1=Tango | first1=Peter J. | last2=Batiuk | first2=Richard A. | title=Deriving Chesapeake Bay Water Quality Standards | journal=JAWRA Journal of the American Water Resources Association | publisher=Wiley | volume=49 | issue=5 | date=2013-09-04 | issn=1093-474X | doi=10.1111/jawr.12108 | pages=1007–1024| bibcode=2013JAWRA..49.1007T | s2cid=102492027 }}</ref> 

There is some desire among the public to return water bodies to pristine, or pre-industrial conditions.<ref>{{Cite web |url=https://www.fs.usda.gov/restoration/Watershed_Restoration/ |title=Watershed Restoration Program |publisher=US Forest Service |location=Washington, DC |access-date=2022-10-05}}</ref> Most current environmental laws focus on the designation of particular uses of a water body. In some countries these designations allow for some [[water contamination]] as long as the particular type of contamination is not harmful to the designated uses. Given the landscape changes (e.g., [[land development]], [[urbanization]], [[clearcutting]] in forested areas) in the [[drainage basin|watersheds]] of many freshwater bodies, returning to pristine conditions would be a significant challenge. In these cases, environmental scientists focus on achieving goals for maintaining healthy ecosystems and may concentrate on the protection of populations of [[endangered species]] and protecting human health.

Regulatory or grading systems related to water quality for bathing include the British [[Bathing Water Regulations 2013]], the European [[Bathing Waters Directive 2006]], and the international [[Blue Flag Beach]] scheme. 
{{Clear}}

==Sampling and measurement{{anchor|Measurement}}==
{{See also|Analysis of water chemistry|analytical chemistry|Water sampling station|Regulation and monitoring of pollution#Water pollution}}
===Sample collection===
{{See also|Environmental monitoring#Sampling methods}}
[[File:WQ sampling station USGS 2004.jpg|thumb|An automated sampling station installed along the East Branch [[Milwaukee River]], [[New Fane, Wisconsin]]. The cover of the 24-bottle autosampler (center) is partially raised, showing the sample bottles inside. The [[autosampler]] collects samples at time intervals, or proportionate to flow over a specified period. The data logger (white cabinet) records temperature, specific conductance, and dissolved oxygen levels.]]
<!-- The beginning of this section is transcribed to [[water pollution]] -->
<section begin=sampling />
The complexity of water quality as a subject is reflected in the many types of measurements of water quality indicators. Some measurements of water quality are most accurately made on-site, because water exists in [[Thermodynamic equilibrium|equilibrium]] with its [[Environment (systems)|surroundings]]. Measurements commonly made on-site and in direct contact with the water source in question include [[temperature]], [[pH]], [[dissolved oxygen]], [[Conductivity (electrolytic)|conductivity]], [[Reduction potential|oxygen reduction potential (ORP)]], [[turbidity]], and [[Secchi disk]] depth.

Sampling of water for physical or chemical testing can be done by several methods, depending on the accuracy needed and the characteristics of the contaminant. Sampling methods include for example simple random sampling, [[stratified sampling]], systematic and grid sampling, adaptive [[cluster sampling]], grab samples, semi-continuous monitoring and continuous, [[passive sampling]], remote surveillance, [[remote sensing]], and [[biomonitoring]]. The use of passive [[Water sampler|samplers]] greatly reduces the cost and the need of infrastructure on the sampling location.

Many contamination events are sharply restricted in time, most commonly in association with rain events. For this reason "grab" samples are often inadequate for fully quantifying contaminant levels.<ref>{{Cite web|title=Sampling - KFUPM School , nature is us - Forums - Tunza Eco Generation|url=https://tunza.eco-generation.org/resourcesView.jsp?boardID=forum1384875145&viewID=7935&searchType=&searchName=&pageNumber=55|access-date=2021-09-19|website=tunza.eco-generation.org|archive-date=7 March 2023|archive-url=https://web.archive.org/web/20230307075538/https://tunza.eco-generation.org/resourcesView.jsp?boardID=forum1384875145&viewID=7935&searchType=&searchName=&pageNumber=55|url-status=dead}}</ref> Scientists gathering this type of data often employ [[Autosampler|auto-sampler]] devices that pump increments of water at either time or [[Discharge (hydrology)|discharge]] intervals.<section end=sampling />

More complex measurements are often made in a [[laboratory]] requiring a water [[Sample (material)|sample]] to be collected, preserved, transported, and analyzed at another location.

==== Issues ====
The process of water sampling introduces two significant problems:
* The first problem is the extent to which the sample may be representative of the water source of interest. Water sources vary with time and with location. The measurement of interest may vary seasonally or from day to night or in response to some activity of man or natural populations of aquatic [[plant]]s and [[animal]]s.<ref name=Goldman>
{{cite book |last1=Goldman |first1=Charles R. |last2=Horne |first2=Alexander J. |title=Limnology |chapter=6. Chemicals and Growth Factors |date=1983 |publisher=McGraw-Hill |isbn=0-07-023651-8}}</ref> The measurement of interest may vary with distances from the water boundary with overlying [[Atmosphere of Earth|atmosphere]] and underlying or confining [[soil]]. The sampler must determine if a single time and location meets the needs of the investigation, or if the water use of interest can be satisfactorily assessed by [[average]]d values of sampling over time and location, or if critical [[maxima and minima]] require individual measurements over a range of times, locations or events. The sample collection procedure must assure correct weighting of individual sampling times and locations where averaging is appropriate.<ref name="Franson">Franson, Mary Ann (1975). ''[https://catalog.hathitrust.org/Record/000494277 Standard Methods for the Examination of Water and Wastewater]'' 14th ed. Washington, DC: American Public Health Association, American Water Works Association & Water Pollution Control Federation. {{ISBN|0-87553-078-8}}</ref>{{rp|39–40}} Where critical maximum or minimum values exist, [[statistics|statistical methods]] must be applied to observed variation to determine an adequate number of samples to assess the [[probability]] of exceeding those critical values.<ref>{{cite report |date=August 1973 |title=Handbook for Monitoring Industrial Wastewater |chapter-url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=20008SJY.txt |publisher=EPA |chapter=Chapter 8. Data Analysis |id=EPA 625/6-73/002}}</ref>
* The second problem occurs as the sample is removed from the water source and begins to establish [[chemical equilibrium]] with its new surroundings – the sample container. Sample containers must be made of [[material]]s with minimal [[Reactivity (chemistry)|reactivity]] with substances to be measured; pre-cleaning of sample containers is important. The water sample may dissolve part of the sample container and any residue on that container, and chemicals dissolved in the water sample may [[sorption|sorb]] onto the sample container and remain there when the water is poured out for analysis.<ref name="Franson" />{{rp|4}} Similar physical and chemical interactions may take place with any [[pump]]s, [[piping]], or intermediate devices used to transfer the water sample into the sample container. Water collected from depths below the surface will normally be held at the reduced [[pressure]] of the atmosphere; so gas [[solvation|dissolved]] in the water will collect at the top of the container. Atmospheric gas above the water may also dissolve into the water sample. Other [[Chemical equilibrium|chemical reaction equilibria]] may change if the water sample changes temperature. Finely divided solid particles formerly [[suspended solids|suspended]] by water [[turbulence]] may settle to the bottom of the sample container, or a solid [[Phase (matter)|phase]] may form from biological growth or [[precipitation (chemistry)|chemical precipitation]]. [[Microorganism]]s within the water sample may biochemically alter [[concentration]]s of [[oxygen]], [[carbon dioxide]], and [[organic compound]]s. Changing carbon dioxide concentrations may alter [[pH]] and change [[solubility]] of chemicals of interest. These problems are of special concern during measurement of chemicals assumed to be significant at very low concentrations.<ref name=Goldman />

[[File:watersampling.JPG|thumb|right|Filtering a manually collected water sample ([[Environmental monitoring#Grab samples|grab sample]]) for analysis]]
Sample preservation may partially resolve the second problem. A common procedure is keeping samples cold to slow the [[reaction rate|rate of chemical reactions]] and phase change, and analyzing the sample as soon as possible; but this merely minimizes the changes rather than preventing them.<ref name="Franson" />{{rp|43–45}} A useful procedure for determining influence of sample containers during delay between sample collection and analysis involves preparation for two artificial samples in advance of the sampling event. One sample container is filled with water known from previous analysis to contain no detectable amount of the chemical of interest. This sample, called a "blank", is opened for exposure to the atmosphere when the sample of interest is collected, then resealed and transported to the laboratory with the sample for analysis to determine if sample collection or holding procedures introduced any measurable amount of the chemical of interest.  The second artificial sample is collected with the sample of interest, but then "spiked" with a measured additional amount of the chemical of interest at the time of collection. The blank ([[negative control]])  and spiked sample ([[Scientific control#Positive|positive control]]) are carried with the sample of interest and analyzed by the same methods at the same times to determine any changes indicating gains or losses during the elapsed time between collection and analysis.<ref>{{cite web |title=Definitions of Quality-Assurance Data |url=https://bqs.usgs.gov/memos/secondary_body.php?Page=aggregated.coding.html |date=2009-08-28 |publisher=USGS, Quality Systems Branch |location=Denver, CO |access-date=5 October 2022 |archive-date=7 March 2023 |archive-url=https://web.archive.org/web/20230307075541/https://bqs.usgs.gov/memos/secondary_body.php?Page=aggregated.coding.html |url-status=dead }}</ref>

===Testing in response to natural disasters and other emergencies===
[[File:EPA water sampling along the Gulf coast (4717896816).jpg|thumb|Testing water in the Gulf of Mexico after the [[Deepwater Horizon oil spill]]]]
After events such as [[earthquake]]s and [[tsunami]]s, there is an immediate response by the aid agencies as relief operations get underway to try and restore basic infrastructure and provide the basic fundamental items that are necessary for survival and subsequent recovery.<ref>{{Cite web |url=https://www.cdc.gov/disasters/tsunamis/waterquality.html |title=Tsunamis: Water Quality |last=Natural Disasters and Severe Weather |publisher=CDC |date=2014-08-13}}</ref> The threat of [[disease]] increases hugely due to the large numbers of people living close together, often in squalid conditions, and without proper sanitation.<ref>{{Cite journal |last1=Furusawa |first1=Takuro |last2=Maki |first2=Norio |last3=Suzuki |first3=Shingo |date=2008-01-01 |title=Bacterial contamination of drinking water and nutritional quality of diet in the areas of the western Solomon Islands devastated by the April 2, 2007 earthquake⁄tsunami |url=https://www.jstage.jst.go.jp/article/tmh/36/2/36_2007-63/_article |journal=Tropical Medicine and Health |volume=36 |issue=2 |pages=65–74 |doi=10.2149/tmh.2007-63 |doi-access=free}}</ref>

After a [[natural disaster]], as far as water quality testing is concerned, there are widespread views on the best course of action to take and a variety of methods can be employed. The key basic water quality parameters that need to be addressed in an emergency are bacteriological indicators of fecal contamination, free [[chlorine]] residual, [[pH]], [[turbidity]] and possibly [[Electrical resistivity and conductivity|conductivity]]/[[total dissolved solids]]. <!-- Spam remnant? completely fails validation!  There are a number of portable water test kits on the market widely used by aid and relief agencies for carrying out such testing.--> There are many decontamination methods.<ref>{{cite journal| last1=Hanaor| first1=Dorian A. H.| last2=Sorrell | first2=Charles C.| title= Sand Supported Mixed-Phase TiO<sub>2</sub> Photocatalysts for Water Decontamination Applications| journal= Advanced Engineering Materials| year=2014| volume=16| issue=2| pages=248–254|doi=10.1002/adem.201300259| arxiv=1404.2652| bibcode=2014AdvEM..16..248H| s2cid=118571942}}</ref><ref>{{cite report |date=April 2010 |title=Method 1680: Fecal Coliforms in Sewage Sludge (Biosolids) by Multiple-Tube Fermentation using Lauryl Tryptose Broth (LTB) and EC Medium |url=https://www.epa.gov/cwa-methods/approved-cwa-microbiological-methods-wastewater-and-sewage-sludge |publisher=EPA |id=EPA 821-R-10-003}}</ref>

After major natural disasters, a considerable length of time might pass before water quality returns to pre-disaster levels. For example, following the [[2004 Indian Ocean tsunami]] the Colombo-based [[International Water Management Institute]] (IWMI) monitored the effects of saltwater and concluded that the wells recovered to pre-tsunami drinking water quality one and a half years after the event.<ref>International Water Management Institute, Colombo, Sri Lanka (2010). [http://www.iwmi.cgiar.org/Publications/Success_Stories/PDF/2010/Issue%207%20-%20Helping_restore_the_quality_of_drinking_water_after_the_tsunami.pdf "Helping restore the quality of drinking water after the tsunami."] ''Success Stories.'' Issue 7. {{doi|10.5337/2011.0030}}</ref> IWMI developed protocols for cleaning wells contaminated by saltwater; these were subsequently officially endorsed by the [[World Health Organization]] as part of its series of Emergency Guidelines.<ref>WHO (2011). [https://www.who.int/water_sanitation_health/hygiene/envsan/technotes/en/ "WHO technical notes for emergencies."] {{webarchive|url=https://web.archive.org/web/20160212053301/http://www.who.int/water_sanitation_health/hygiene/envsan/technotes/en/ |date=12 February 2016 }} Water Engineering Development Centre, Loughborough University, Leicestershire, UK.</ref>

===Chemical analysis===
[[File:GCMS open.jpg|thumb|right|A [[Gas chromatography–mass spectrometry|gas chromatograph-<br/>mass spectrometer]] measures [[pesticide]]s and other [[Organic compound|organic]] pollutants.]]
The simplest methods of [[Analytical chemistry|chemical analysis]] are those measuring [[chemical element]]s without respect to their form. Elemental analysis for [[oxygen]], as an example, would indicate a concentration of 890 g/L ([[Gram|grams]] per [[litre]]) of water sample because oxygen (O) has 89% mass of the water molecule (H<sub>2</sub>O). The method selected to measure [[dissolved oxygen]] should differentiate between [[Diatomic molecule|diatomic]] oxygen and oxygen combined with other elements. The comparative simplicity of elemental analysis has produced a large amount of sample data and water quality criteria for elements sometimes identified as [[Heavy metal (chemistry)|heavy metals]]. Water analysis for heavy metals must consider soil particles suspended in the water sample. These suspended soil particles may contain measurable amounts of metal. Although the particles are not [[solvation|dissolved]] in the water, they may be consumed by people drinking the water. Adding [[acid]] to a water sample to prevent loss of dissolved metals onto the sample container may dissolve more metals from suspended soil particles. [[Filtration]] of soil particles from the water sample before acid addition, however, may cause loss of dissolved metals onto the filter.<ref>State of California Environmental Protection Agency ''Representative Sampling of Ground Water for Hazardous Substances'' (1994) pp.&nbsp;23–24</ref> The complexities of differentiating similar [[organic chemistry|organic molecules]] are even more challenging.
[[File:PSA 2.jpg|thumb|[[Atomic fluorescence spectroscopy]] is used to measure [[Mercury (element)|mercury]] and other heavy metals.]]
Making these complex measurements can be expensive. Because direct measurements of water quality can be expensive, ongoing monitoring programs are typically conducted and results released by [[Government agency|government agencies]]. However, there are local volunteer programs and resources available for some general assessment.<ref>An example of a local government-sponsored volunteer monitoring program: {{cite web |url=https://www.montgomerycountymd.gov/water/streams/monitoring.html |title=Monitoring Our Waters |author=<!--Not stated--> |website=Watershed Restoration |publisher=Montgomery County Department of Environmental Protection |location=Rockville, MD |access-date=2018-11-11}}.</ref> Tools available to the general public include on-site test kits, commonly used for home [[Aquarium|fish tanks]], and biological assessment procedures.

===Biosensors===
[[Biosensor]]s have the potential for "high sensitivity, selectivity, reliability, simplicity, low-cost and real-time response".<ref>{{cite journal |last1=Ejeian |first1=Fatemeh |last2=Etedali |first2=Parisa |last3=Mansouri-Tehrani |first3=Hajar-Alsadat |last4=Soozanipour |first4=Asieh |last5=Low |first5=Ze-Xian |last6=Asadnia |first6=Mohsen |last7=Taheri-Kafrani |first7=Asghar |last8=Razmjou |first8=Amir |title=Biosensors for wastewater monitoring: A review |journal=Biosensors & Bioelectronics |date=30 October 2018 |volume=118 |pages=66–79 |doi=10.1016/j.bios.2018.07.019 |pmid=30056302 |bibcode=2018BioBi.118...66E |s2cid=51889142 |issn=1873-4235}}</ref> For instance, [[Nanobiotechnology#Bionanotechnology|bionanotechnologists]] reported the development of {{tooltip|2=RNA Output Sensors Activated by Ligand INDuction|ROSALIND 2.0}}, that can detect levels of diverse water pollutants.<ref>{{cite news |title=DNA computer could tell you if your drinking water is contaminated |url=https://www.newscientist.com/article/2308396-dna-computer-could-tell-you-if-your-drinking-water-is-contaminated/ |access-date=16 March 2022 |work=New Scientist}}</ref><ref>{{cite journal |last1=Jung |first1=Jaeyoung K. |last2=Archuleta |first2=Chloé M. |last3=Alam |first3=Khalid K. |last4=Lucks |first4=Julius B. |title=Programming cell-free biosensors with DNA strand displacement circuits |journal=Nature Chemical Biology |date=17 February 2022 |volume=18 |issue=4 |pages=385–393 |doi=10.1038/s41589-021-00962-9 |pmid=35177837 |pmc=8964419 |issn=1552-4469}}</ref>

===Real-time monitoring===
Although water quality is usually sampled and analyzed at laboratories, since the late 20th century there has been increasing public interest in the quality of drinking water provided by municipal systems. Many water utilities have developed systems to collect real-time data about source water quality. In the early 21st century, a variety of sensors and remote monitoring systems have been deployed for measuring water pH, turbidity, dissolved oxygen and other parameters.<ref>{{cite report |title=Distribution System Water Quality Monitoring: Sensor Technology Evaluation Methodology and Results |url=https://www.epa.gov/waterresilience/online-water-quality-monitoring-resources |date=October 2009 |publisher=EPA |id=EPA 600/R-09/076}}</ref> Some remote sensing systems have also been developed for monitoring ambient water quality in riverine, estuarine and coastal water bodies.<ref>{{cite web |title=Water Quality Monitoring |url=https://meri.njmeadowlands.gov/projects/continuous-water-monitoring-stations/ |date=2018-08-06 |publisher=Meadowlands Environmental Research Institute |location=Lyndhurst, New Jersey |access-date=6 December 2018 |archive-date=7 March 2023 |archive-url=https://web.archive.org/web/20230307075545/https://meri.njmeadowlands.gov/projects/continuous-water-monitoring-stations/ |url-status=dead }}</ref><ref>{{cite web |title=Eyes on the Bay |url=http://eyesonthebay.dnr.maryland.gov |publisher=Maryland Department of Natural Resources |location=Annapolis, MD |id=Chesapeake Bay |access-date=2018-12-05}}</ref>
[[File:Electrical conductivity meter.jpg|thumb|right|An [[electrical conductivity meter]] is used to measure [[total dissolved solids]].]]
The following is a list of indicators often measured by situational category:
* [[Alkalinity]]
* [[Color of water]]
* [[pH]]
* Taste and odor ([[geosmin]], [[2-Methylisoborneol]] (MIB), etc.)
* Dissolved metals and salts ([[sodium]], [[chloride]], [[potassium]], [[calcium]], [[manganese]], [[magnesium]])
* Microorganisms such as [[fecal coliform]] bacteria (''Escherichia coli''), [[Cryptosporidium]], and [[Giardia lamblia]]; ''see'' [[Bacteriological water analysis]]
* Dissolved metals and metalloids ([[lead]], [[mercury (element)|mercury]], [[arsenic]], etc.)
* Dissolved organics: [[colored dissolved organic matter]] (CDOM), [[dissolved organic carbon]] (DOC)
* [[Radon]]
* [[Heavy metals]]
* [[Pharmaceutical]]s
* [[Hormone]] analogs

===Environmental indicators===
{{See also|Environmental indicator|Wastewater quality indicators|Salinity}}

====Physical indicators====
{{Col-start}}
{{Col-2}}
* Water [[temperature]]
* Specific conductance or [[electrical conductance]] (EC) or conductivity
* [[Total suspended solids]] (TSS)
* [[Secchi depth|Transparency]] or [[turbidity]]
* [[Water clarity]]
{{Col-2}}
* [[Total dissolved solids]] (TDS)
* [[Odour]] of water
* [[Color of water]] (such as [[Forel-Ule scale]] or [[Pt/Co scale]])
* [[Taste]] of water
{{Col-end}}

====Chemical indicators====
{{Col-start}}
{{Col-2}}
* [[Alkalinity]]
* [[Biochemical oxygen demand]] (BOD)
* [[Chemical oxygen demand]] (COD)
* [[Dissolved oxygen]] (DO)
* [[Hard water|Total hardness]] (TH)
* [[Heavy metals]]
* [[Nitrate]]
{{Col-2}}
* [[Orthophosphate]]s
* [[pH]]
* [[Pesticide]]s
* [[Residual sodium carbonate index]] (RSC)
* [[Sodium adsorption ratio]] (SAR)
* [[Surfactant]]s
{{Col-end}}

====Biological indicators====
{{See also|Biological integrity|Index of biological integrity}}
{{Col-start}}
{{Col-2}}
* [[Ephemeroptera]] 
* [[Plecoptera]] 
* [[Mollusca]]
* [[Trichoptera]]
* ''[[Escherichia coli]]'' (E. coli)
{{Col-2}}
* [[Coliform bacteria]]
* ''[[Pimephales promelas]]'' (fathead minnow)
* ''[[Americamysis bahia]]'' (Mysid shrimp)
* [[Sea urchin]]
* [[Protists]], e.g. ''[[Paratrimastix pyriformis]]''
{{Col-end}}

[[Biological indicator|Biological monitoring]] metrics have been developed in many places, and one widely used family of measurements for freshwater is the presence and abundance of members of the insect orders [[Ephemeroptera]], [[Plecoptera]] and [[Trichoptera]] (EPT) (of [[benthic]] [[macroinvertebrate]]s whose common names are, respectively, mayfly, stonefly and caddisfly). EPT indexes will naturally vary from region to region, but generally, within a region, the greater the number of taxa from these orders, the better the water quality. Organisations in the United States, such as EPA. offer guidance on developing a monitoring program and identifying members of these and other aquatic insect orders. Many US wastewater dischargers (e.g., factories, power plants, [[refineries]], mines, municipal [[sewage treatment]] plants) are required to conduct periodic whole effluent toxicity (WET) tests.<ref name="WET-methods">{{cite web |url=https://www.epa.gov/cwa-methods/whole-effluent-toxicity-methods |title=Whole Effluent Toxicity Methods |author=<!--Not stated--> |date=2020-08-01 |website=Clean Water Act Analytical Methods |publisher=EPA}}</ref><ref>{{cite report |date=October 2002 |title=Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms |url=https://www.epa.gov/cwa-methods/acute-toxicity-wet-methods |publisher=EPA |id=EPA-821-R-02-012}}</ref>

Individuals interested in monitoring water quality who cannot afford or manage lab scale analysis can also use biological indicators to get a general reading of water quality. One example is the IOWATER volunteer water monitoring program of [[Iowa]], which includes an EPT indicator key.<ref>IOWATER (Iowa Department of Natural Resources). Iowa City, IA (2005). [http://www.iowater.net/Publications/BMIKey2Edvmay05.pdf "Benthic Macroinvertebrate Key."]</ref>

Bivalve molluscs are largely used as [[bioindicators]] to monitor the health of aquatic environments in both fresh water and the marine environments. Their population status or structure, physiology, behaviour or the level of contamination with elements or compounds can indicate the state of contamination status of the ecosystem. They are particularly useful since they are sessile so that they are representative of the environment where they are sampled or placed. A typical project is the U.S. [[Mussel Watch Program]]me,<ref>{{cite web |url=http://ccma.nos.noaa.gov/about/coast/nsandt/musselwatch.aspx |title=Center for Coastal Monitoring and Assessment: Mussel Watch Contaminant Monitoring |publisher=Ccma.nos.noaa.gov |date=2014-01-14 |access-date=2015-09-04 |url-status=dead |archive-url=https://web.archive.org/web/20150907012135/http://ccma.nos.noaa.gov/about/coast/nsandt/musselwatch.aspx |archive-date=7 September 2015}}</ref> but today they are used worldwide.

The Southern African Scoring System (SASS) method is a biological water quality monitoring system based on the presence of benthic macroinvertebrates (EPT). The SASS [[aquatic biomonitoring]] tool has been refined over the past 30 years and is now on the fifth version (SASS5) which has been specifically modified in accordance with international standards, namely the [[ISO/IEC 17025]] protocol.<ref>Dickens CWS and Graham PM. 2002. [http://www.dwa.gov.za/iwqs/rhp/methods/dickens%20and%20graham.pdf The Southern Africa Scoring System (SASS) version 5 rapid bioassessment for rivers] "African Journal of Aquatic Science", 27:1–10.</ref> The SASS5 method is used by the South African [[Department of Water Affairs]] as a standard method for River Health Assessment, which feeds the national River Health Programme and the national Rivers Database.

==Climate change impacts==
{{excerpt|Water security#Reduced water quality due to climate change|file=no}}

==Standards and reports==
In the setting of standards, agencies make political and technical/scientific decisions based on how the water will be used.<ref>{{cite web |author=<!--Staff writer(s); no by-line.--> |title=What Are Water Quality Standards? |url=https://www.epa.gov/wqs-tech/what-are-water-quality-standards |date=2022-04-14 |website=Standards for Water Body Health |publisher=EPA}}</ref> In the case of natural [[Body of water|water bodies]], agencies also make some reasonable estimate of pristine conditions. Natural water bodies will vary in response to a region's environmental conditions, whereby water composition is influenced by the surrounding geological features, sediments, and rock types, [[topography]], [[hydrology]], and climate.<ref>{{Cite web |last1=Daniels |first1=Mike|last2=Scott |first2=Thad |last3=Haggard |first3=Brian |last4=Sharpley |first4=Andrew |last5=Daniel |first5=Tommy |date=2009 |title=What is Water Quality? |url=https://www.uaex.edu/publications/pdf/FSA-9528.pdf|website=University of Arkansas Division of Agriculture|access-date=2 December 2020|archive-date=1 December 2020|archive-url=https://web.archive.org/web/20201201185338/https://www.uaex.edu/publications/pdf/FSA-9528.pdf|url-status=dead}}</ref> [[Environmental science|Environmental scientists]] and [[Aqueous geochemistry|aqueous geochemists]] work to interpret the parameters and environmental conditions that impact the water quality of a region, which in turn helps to identify the sources and fates of [[contaminant]]s. [[Environmental lawyers]] and [[policy]]makers work to define [[legislation]] with the intention that water is maintained at an appropriate quality for its identified use.

Another general perception of water quality is that of a simple property that tells whether water is [[pollution|polluted]] or not. In fact, water quality is a complex subject, in part because water is a complex medium intrinsically tied to the [[ecology]], [[geology]], and [[Anthropogenic effect|anthropogenic activities]] of a region. [[Industrial sector|Industrial]] and [[Commerce|commercial]] activities (e.g. [[manufacturing]], [[mining]], [[construction]], [[transport]]) are a major cause of [[water pollution]] as are [[surface runoff|runoff]] from [[farm|agricultural]] areas, [[urban runoff]] and discharge of treated and untreated [[sewage]].{{Citation needed|date=April 2023}}

{{See also||Drinking water quality standards}}

=== International ===

* The [[World Health Organization]] (WHO) published updated guidelines for drinking-water quality (GDWQ) in 2017.<ref name="WHO DW quality"/>
*The [[International Organization for Standardization]] (ISO) published {{when|date=June 2016}} regulation of water quality in the section of ICS 13.060,<ref name=13wq>{{cite web |last=International Organization for Standardization (ISO) |title=13.060: Water quality |location=Geneva |url=http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_ics_browse.htm?ICS1=13&ICS2=060 |access-date=2011-07-04}}</ref> ranging from water sampling, drinking water, industrial class water, sewage, and examination of water for chemical, physical or biological properties. ICS 91.140.60 covers the standards of water supply systems.<ref name=91wss>{{cite web |last=ISO |title=91.140.60: Water supply systems |url=http://www.iso.org/iso/catalogue_ics_browse?ICS1=91&ICS2=140&ICS3=60&&published=on |access-date=2011-07-04}}</ref>

===National specifications for ambient water and drinking water===
<!-- add in alphanumeric order -->

====European Union====
{{Further|Water supply and sanitation in the European Union}}
The water policy of the [[European Union]] is primarily codified in three [[European Union directive|directives]]:
*[[Directive on Urban Waste Water Treatment]] (91/271/EEC) of 21 May 1991 concerning discharges of municipal and some industrial [[wastewater]]s;
*[[Water supply and sanitation in the European Union#Drinking water directive of 1998|The Drinking Water Directive]] (98/83/EC) of 3 November 1998 concerning potable water quality;
*[[Water Framework Directive]] (2000/60/EC) of 23 October 2000 concerning [[water resources]] management.

====India====
* [[Indian Council of Medical Research]] (ICMR) Standards for Drinking Water.

====South Africa====
{{Further|Water supply and sanitation in South Africa}}
Water quality guidelines for South Africa are grouped according to potential user types (e.g. domestic, industrial) in the 1996 Water Quality Guidelines.<ref>Republic of South Africa, Department of Water Affairs, Pretoria (1996). [http://www.dwaf.gov.za/IWQS/wq_guide/index.html "Water quality guidelines for South Africa: First Edition 1996."]</ref> Drinking water quality is subject to the South African National Standard (SANS) 241 Drinking Water Specification.<ref>Hodgson K, Manus L. A drinking water quality framework for South Africa. Water SA. 2006;32(5):673–678 [http://www.ajol.info/index.php/wsa/article/viewFile/47853/34223].</ref>

====United Kingdom====
In England and Wales acceptable levels for drinking water supply are listed in the "Water Supply (Water Quality) Regulations 2000."<ref>National Archives, London, UK. [http://www.legislation.gov.uk/uksi/2000/3184/contents/made "The Water Supply (Water Quality) Regulations 2000."] 2000 No. 3184. 2000-12-08.</ref>

====United States====
{{Main|Drinking water quality in the United States|Drinking water quality legislation of the United States|Water supply and sanitation in the United States}}
In the United States, [[Clean Water Act#Water Quality Standards Program|Water Quality Standards]] are defined by state agencies for various water bodies, guided by the desired uses for the water body (e.g., fish habitat, drinking water supply, recreational use).<ref>U.S. Clean Water Act, Section 303, {{USC|33|1313}}.</ref> The [[Clean Water Act]] (CWA) requires each governing jurisdiction (states, territories, and covered tribal entities) to submit a set of biennial reports on the quality of water in their area. These reports are known as the 303(d) and 305(b) reports, named for their respective CWA provisions, and are submitted to, and approved by, EPA.<ref>U.S. Clean Water Act, Section 303(d), {{USC|33|1313}}; Section 305(b), {{USC|33|1315(b)}}.</ref> These reports are completed by the governing jurisdiction, typically a [[:Category:State environmental protection agencies of the United States|state environmental agency]]. EPA recommends that each state submit a single "Integrated Report" comprising its list of impaired waters and the status of all water bodies in the state.<ref>{{cite web |title=Overview of Listing Impaired Waters under CWA Section 303(d) |author=<!--Staff writer(s); no by-line.--> |url=https://www.epa.gov/tmdl/overview-listing-impaired-waters-under-cwa-section-303d |website=Impaired Waters and TMDLs |date=2022-08-31 |publisher=EPA}}</ref> The ''National Water Quality Inventory Report to Congress'' is a general report on water quality, providing overall information about the number of miles of streams and rivers and their aggregate condition.<ref>{{cite web |url=https://www.epa.gov/waterdata/national-water-quality-inventory-report-congress |title=National Water Quality Inventory Report to Congress |author=<!--Staff writer(s); no by-line.--> |date=2021-12-07 |website=Water Data and Tools |publisher=EPA}}</ref> The CWA requires states to adopt standards for each of the possible designated uses that they assign to their waters. Should evidence suggest or document that a stream, river or lake has failed to meet the water quality criteria for one or more of its designated uses, it is placed on a list of impaired waters. Once a state has placed a water body on this list, it must develop a management plan establishing [[Total Maximum Daily Load]]s (TMDLs) for the pollutant(s) impairing the use of the water. These TMDLs establish the reductions needed to fully support the designated uses.<ref>More information about water quality in the United States is available on EPA's [https://www.epa.gov/waterdata/hows-my-waterway "How's My Waterway"] website.</ref>

Drinking water standards, which are applicable to [[public water system]]s, are issued by EPA under the [[Safe Drinking Water Act]].<ref name="EPA DW reqts"/>

==See also==
{{Portal|Environment|Water}}
{{div col|colwidth=35em}}
* {{annotated link|Aquatic toxicology}}
* {{annotated link|Permanganate index}}
* {{annotated link|Stiff diagram}}
* {{annotated link|Water clarity}}
* {{annotated link|Water quality modelling}}
* {{annotated link|Water testing}}
* {{annotated link|Water treatment}}
{{div col end}}

==References==
{{Reflist}}

==External links==

* [http://www.gemstat.org Global Freshwater Quality Database (GEMStat)] – United Nations environment program
* [https://ec.europa.eu/environment/water/news.html Water policy in the European Union]
* [https://www.cdc.gov/healthywater/drinking/public/water_quality.html U.S. Centers for Disease Control and Prevention (CDC)] – Drinking water quality and testing (United States)
* [https://www.epa.gov/waterdata U.S. Environmental Protection Agency] – Water Data and Tools of the USEPA
* [http://water.usgs.gov/nawqa U.S. Geological Survey] – National Water Quality Assessment Program of the USGS
{{Webarchive|url=https://web.archive.org/web/20180324205603/http://awra.org/ |date=24 March 2018 }} – Professional association

{{Natural resources}}
{{Pollution}}
{{Authority control}}

{{DEFAULTSORT:Water Quality}}
[[Category:Environmental science]]
[[Category:Water]]
[[Category:Water management]]
[[Category:Water pollution]]
[[Category:Water supply]]
[[Category:Water quality indicators|*]]