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Water pollution

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Raw sewage and industrial waste in the New River as it passes from Mexicali (Mexico) to Calexico, California

Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, in such a manner that negatively affects its legitimate uses.[1]: 6  Water pollution reduces the ability of the body of water to provide the ecosystem services that it would otherwise provide. Water bodies include for example lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants are introduced into these water bodies. For example, releasing inadequately treated wastewater into natural waters can lead to degradation of these aquatic ecosystems. All plants and organisms living in or being exposed to polluted water bodies can be impacted. The effects can damage individual species and impact the natural biological communities they are part of. Water pollution can also lead to water-borne diseases for people using polluted water for drinking, bathing, washing or irrigation.[2]

Water pollution can be classified as surface water pollution (for example lakes, streams, estuaries, and parts of the ocean in marine pollution) or groundwater pollution. Sources of water pollution are either point sources or non-point sources. Point sources have one identifiable cause, such as a storm drain or a wastewater treatment plant. Non-point sources are more diffuse, such as agricultural runoff.[3] Pollution is the result of the cumulative effect over time. Supplying clean drinking water is an important ecosystem service provided by some freshwater systems, but approximately 785 million people in the world do not have access to clean drinking water because of pollution.[4]

Pollution may take the form of toxic substances (e.g., oil, metals, plastics, pesticides, persistent organic pollutants, industrial waste products), stressful conditions (e.g., changes of pH, hypoxia or anoxia, stressful temperatures, excessive turbidity, unpleasant taste or odor, and changes of salinity), or pathogenic organisms. Contaminants may include organic and inorganic substances. Heat can also be a pollutant, and this is called thermal pollution. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers.

Water pollution is measured by analyzing water samples and testing for a range of physical, chemical and biological parameters. Control of water pollution requires appropriate infrastructure and management plans as well as legislation. Technology solutions can include improving sanitation, sewage treatment, industrial wastewater treatment, agricultural wastewater treatment, erosion control, sediment control and control of urban runoff (including stormwater management). Effective control of urban runoff includes reducing speed and quantity of flow.


Pollution in the Lachine Canal, Canada

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".[1]: 6  Therefore, pollution is associated with concepts attributed to humans, namely the negative alterations and the uses of the water body. Water is typically referred to as polluted when it is impaired by anthropogenic contaminants. Due to these contaminants it either does not support a human use, such as drinking water, or undergoes a marked shift in its ability to support its biotic communities, such as fish.



Water pollution is a major global environmental problem because it can result in the degradation of aquatic ecosystems. 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 man-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.

There is concern that water pollution can damage phytoplankton in the oceans who produce 70% of oxygen and remove a large part of carbon dioxide from the atmosphere.[5]

Public health and waterborne diseases

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).[6]

Eutrophication from nitrogen pollution

Nitrogen pollution (a form of water pollution where excessive amounts of nutrients are added to a water body), 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. Depending on the degree of eutrophication, subsequent negative environmental effects such as anoxia (oxygen depletion) and severe reductions in water quality may occur, affecting fish and other animal populations.[1]: 131 

Eutrophication (from Greek eutrophos, "well-nourished")[7] is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients. It has also been defined as "nutrient-induced increase in phytoplankton productivity".[8]: 459  Water bodies with very low nutrient levels are termed oligotrophic and those with moderate nutrient levels are termed mesotrophic. Advanced eutrophication may also be referred to as dystrophic and hypertrophic conditions.[9] Eutrophication in freshwater ecosystems is almost always caused by excess phosphorus.[10]

Prior to human interference, this was, and continues to be, a very slow natural process in which nutrients, especially phosphorus compounds and organic matter, accumulate in water bodies.[11] These nutrients derive from degradation and solution of minerals in rocks and by the effect of lichens, mosses and fungi actively scavenging nutrients from rocks.[12] Anthropogenic or cultural eutrophication is often a much more rapid process in which nutrients are added to a water body from any of a wide variety of polluting inputs including untreated or partially treated sewage, industrial wastewater and fertilizer from farming practices. Nutrient pollution, a form of water pollution, is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrogen or phosphorus, stimulate algal and aquatic plant growth.

Ocean acidification

Ocean acidification is another impact of water pollution.

Ocean acidification is the ongoing decrease in the pH value of the Earth's oceans, caused by the uptake of carbon dioxide (CO
) from the atmosphere.[13] The main cause of ocean acidification is the burning of fossil fuels. Ocean acidification is one of several effects of climate change on oceans. Seawater is slightly basic (meaning pH > 7), and ocean acidification involves a shift towards pH-neutral conditions rather than a transition to acidic conditions (pH < 7).[14] The concern with ocean acidification is that it can lead to the decreased production of the shells of shellfish and other aquatic life with calcium carbonate shells, as well as some other physiological challenges for marine organisms. The calcium carbonate shelled organisms can not reproduce under high saturated acidotic waters. An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes.[15][16] Some of it reacts with the water to form carbonic acid. Some of the resulting carbonic acid molecules dissociate into a bicarbonate ion and a hydrogen ion, thus increasing ocean acidity (H+ ion concentration).

Contaminants and their sources


If the water pollution stems from sewage (municipal wastewater), the main pollutants are: suspended solids, biodegradable organic matter, nutrients and pathogenic organisms.[1]: 6 

Pollutants and their effects (sources of these pollutants are municipal and industrial wastewater, urban runoff, agricultural and pasture activities). Adapted from [1]: 7 
Pollutant Main representative parameter Possible effect of the pollutant
Suspended solids Total suspended solids
Biodegradable organic matter Biological oxygen demand
  • Oxygen consumption
  • Death of fish
  • Septic conditions
Pathogens Waterborne diseases
Non-biodegradable organic matter
Inorganic dissolved solids

Pathogens from sewage and agriculture

Poster to teach people in South Asia about human activities leading to the pollution of water sources

Disease-causing microorganisms are referred to as pathogens. The major groups of pathogenic organisms are: (a) bacteria, (b) viruses, (c) protozoans and (d) helminths. [1]: 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), fecal coliforms (FC) or thermotolerant coliforms, escherichia coli (EC).[1]: 47 

Pathogens can produce waterborne diseases in either human or animal hosts.[18] 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, parasitic worms including the Schistosoma type.[19]

The source of high levels of pathogens in water bodies can be from human feces (due to open defecation), sewage, blackwater, manure that has found its way into the water body. The cause for this can be lack of sanitation 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)[20] during storm events and intensive agriculture (poorly managed livestock operations).

Muddy river polluted by sediment.

Non-biodegradable organic compounds

Contaminants may include non-biodegradable organic substances. Many of these chemical substances are toxic.[21]: 229 

A garbage collection boom to reduce pollution in an urban stream in Auckland, New Zealand.

The following compounds can all reach water bodies via raw sewage or even treated sewage discharges (this is because removal of these "micropollutants" is complex and costly (see also below under Control and Reduction)):

Very low levels of specific contaminants in raw or treated sewage, including hormones (from animal husbandry and residue from human hormonal contraception methods) and synthetic materials such as phthalates that mimic hormones in their action, can have an unpredictable adverse impact on the natural biota and potentially on humans if the water is treated and utilized for drinking water.[29][30][31]

Persistent organic pollutant

Persistent organic pollutants (POPs), sometimes known as "forever chemicals" are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes.[32] It is a toxic chemical that adversely affect human health and the environment around the world. Because they can be transported by wind and water, most POPs generated in one country can and do affect people and wildlife far from where they are used and released. The effect of POPs on human and environmental health was discussed, with intention to eliminate or severely restrict their production, by the international community at the Stockholm Convention on Persistent Organic Pollutants in 2001. The United States has taken strong domestic action to reduce emissions of POPs. For example, none of the original POPs pesticides listed in the Stockholm Convention is registered for sale and distribution in the United States today and in 1978, Congress prohibited the manufacture of PCBs and severely restricted the use of remaining PCB stocks. In addition, since 1987, EPA and the states have effectively reduced environmental releases of dioxins and furans to land, air, and water from U.S. sources.

Many POPs are currently or were in the past used as pesticides, solvents, pharmaceuticals, and industrial chemicals.[32] Although some POPs arise naturally (e.g. from volcanoes), most are man-made.[33]

Environmental persistent pharmaceutical pollutants

Water pollution due to environmental persistent pharmaceutical pollutants can have wide-ranging consequences:

The environmental effect of pharmaceuticals and personal care products (PPCPs) is being investigated since at least the 1990s. PPCPs include substances used by individuals for personal health or cosmetic reasons and the products used by agribusiness to boost growth or health of livestock. More than twenty million tons of PPCPs are produced every year.[34] The European Union has declared pharmaceutical residues with the potential of contamination of water and soil to be "priority substances".[3]

PPCPs have been detected in water bodies throughout the world. More research is needed to evaluate the risks of toxicity, persistence, and bioaccumulation, but the current state of research shows that personal care products impact over the environment and other species, such as coral reefs[35][36][37] and fish.[38][39] PPCPs encompass environmental persistent pharmaceutical pollutants (EPPPs) and are one type of persistent organic pollutants. They are not removed in conventional sewage treatment plants but require a fourth treatment stage which not many plants have.[34]

Inorganic contaminants

Inorganic water pollutants include for example:

Contaminants from industrial wastewater

If the pollution stems from industrial wastewater, then pollutants may include:

The composition of industrial wastewater varies widely. This is a partial list of chemical or physical pollutants that may be contained in industrial wastewater:

Solid waste and plastics

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 term marine debris is used in the context of pollution of oceans.

Marine debris, also known as marine litter, is human-created waste that has deliberately or accidentally been released in a sea or ocean. Floating oceanic debris tends to accumulate at the center of gyres and on coastlines, frequently washing aground, when it is known as beach litter or tidewrack. Deliberate disposal of wastes at sea is called ocean dumping. Naturally occurring debris, such as driftwood and drift seeds, are also present.

With the increasing use of plastic, human influence has become an issue as many types of (petrochemical) plastics do not biodegrade quickly, as would natural or organic materials.[45] The largest single type of plastic pollution (~10 %) and majority of large plastic in the oceans is discarded and lost nets from the fishing industry.[46] Waterborne plastic poses a serious threat to fish, seabirds, marine reptiles, and marine mammals, as well as to boats and coasts.[47] Dumping, container spillages, litter washed into storm drains and waterways and wind-blown landfill waste all contribute to this problem. This increased water pollution has caused serious negative effects such as ghost nets capturing animals, concentration of plastic debris in massive marine garbage patches, and increasing concentrations of contaminants in the food chain.


A growing concern regarding plastic pollution in the marine ecosystem is the use of microplastics. Microplastics are little beads of plastic less than 5 millimeters wide,[49] and they are commonly found in hand soaps, face cleansers, and other exfoliators. When these products are used, the microplastics go through the water filtration system and into the ocean, but because of their small size they are likely to escape capture by the preliminary treatment screens on wastewater plants.[50] These beads are harmful to the organisms in the ocean, especially filter feeders, because they can easily ingest the plastic and become sick. The microplastics are such a concern because it is difficult to clean them up due to their size, so humans can try to avoid using these harmful plastics by purchasing products that use environmentally safe exfoliates.

Because plastic is so widely used across the planet, microplastics have become widespread in the marine environment. For example, microplastics can be found on sandy beaches[51] and surface waters[52] as well as in the water column and deep sea sediment. Microplastics are also found within the many other types of marine particles such as dead biological material (tissue and shells) and some soil particles (blown in by wind and carried to the ocean by rivers). Upon reaching marine environments, the fate of microplastics is subject to naturally occurring drivers, such as winds and surface oceanic currents. Numerical models are able to trace small plastic debris (micro- and meso-plastics) drifting in the ocean,[53] thus predicting their fate.
Microplastics have been widely detected in the world's aquatic environments.[54][55] The first study on microplastics in freshwater ecosystems was published in 2011 that found an average of 37.8 fragments per square meter of Lake Huron sediment samples. Additionally, studies have found MP (microplastic) to be present in all of the Great Lakes with an average concentration of 43,000 MP particle km−2.[56] Microplastics have also been detected in freshwater ecosystems outside of the United States. In Canada, a three-year study found a mean microplastic concentration of 193,420 particles km−2 in Lake Winnipeg. None of the microplastics detected were micro-pellets or beads and most were fibers resulting from the breakdown of larger particles, synthetic textiles, or atmospheric fallout.[57] The highest concentration of microplastic ever discovered in a studied freshwater ecosystem was recorded in the Rhine river at 4000 MP particles kg−1.[58]

Types of surface water pollution

A polluted river draining an abandoned copper mine on Anglesey

Pollution of rivers, lakes and oceans

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.[59] 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.

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.

Marine pollution

Marine pollution occurs when substances used or spread by humans, such as industrial, agricultural and residential waste, particles, noise, excess carbon dioxide or invasive organisms enter the ocean and cause harmful effects there. The majority of this waste (80%) comes from land-based activity, although marine transportation significantly contributes as well.[60] Since most inputs come from land, either via the rivers, sewage or the atmosphere, it means that continental shelves are more vulnerable to pollution. Air pollution is also a contributing factor by carrying off iron, carbonic acid, nitrogen, silicon, sulfur, pesticides or dust particles into the ocean.[61] The pollution often comes from nonpoint sources such as agricultural runoff, wind-blown debris, and dust. These nonpoint sources are largely due to runoff that enters the ocean through rivers, but wind-blown debris and dust can also play a role, as these pollutants can settle into waterways and oceans.[62] Pathways of pollution include direct discharge, land runoff, ship pollution, atmospheric pollution and, potentially, deep sea mining.

The types of marine pollution can be grouped as pollution from marine debris, plastic pollution, including microplastics, ocean acidification, nutrient pollution, toxins and underwater noise. Plastic pollution in the ocean is a type of marine pollution by plastics, ranging in size from large original material such as bottles and bags, down to microplastics formed from the fragmentation of plastic material. Marine debris is mainly discarded human rubbish which floats on, or is suspended in the ocean. Plastic pollution is harmful to marine life.

Nutrient pollution

Nutrient pollution caused by Surface runoff of soil and fertilizer during a rain storm

Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth.[63] Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion. Raw sewage is a large contributor to cultural eutrophication since sewage is high in nutrients. Releasing raw sewage into a large water body is referred to as sewage dumping, and still occurs all over the world. Excess reactive nitrogen compounds in the environment are associated with many large-scale environmental concerns. These include eutrophication of surface waters, harmful algal blooms, hypoxia, acid rain, nitrogen saturation in forests, and climate change.[64]

Since the agricultural boom in the 1910s and again in the 1940s to match the increase in food demand, agricultural production relies heavily on the use of fertilizers.[65] Fertilizer is a natural or chemically modified substance that helps soil become more fertile. These fertilizers contain high amounts of phosphorus and nitrogen, which results in excess amounts of nutrients entering the soil. Nitrogen, phosphorus and potassium are the "Big 3" primary nutrients in commercial fertilizers, each of these fundamental nutrients play a key role in plant nutrition.[66] When nitrogen and phosphorus are not fully utilized by the growing plants, they can be lost from the farm fields and negatively impact air and downstream water quality.[67] These nutrients can eventually end up in aquatic ecosystems and are a contributor to increased eutrophication.[68] When farmers spread their fertilizer whether it is organic or synthetically made most of the fertilizer will turn into runoff that collects downstream generating cultural eutrophication.[69]

Thermal pollution

The Brayton Point Power Station in Massachusetts discharges heated water to Mount Hope Bay.
Thermal pollution, sometimes called "thermal enrichment," is the degradation of water quality by any process that changes ambient water temperature. Thermal pollution is the rise or fall in the temperature of a natural body of water caused by human influence. Thermal pollution, unlike chemical pollution, results in a change in the physical properties of water. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. Urban runoffstormwater discharged to surface waters from rooftops, roads and parking lots—and reservoirs can also be a source of thermal pollution.[70] Thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers.

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.[71]: 179 [21]: 375 

Oil spills

An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into the ocean or coastal waters, but spills may also occur on land. Oil spills may be due to releases of crude oil from tankers, offshore platforms, drilling rigs and wells, as well as spills of refined petroleum products (such as gasoline, diesel) and their by-products, heavier fuels used by large ships such as bunker fuel, or the spill of any oily refuse or waste oil.


The introduction of aquatic invasive organisms is a form of water pollution as well. It causes biological pollution.[72]

Groundwater pollution

Groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwanted constituent, contaminant, or impurity in the groundwater, in which case it is more likely referred to as contamination rather than pollution. Pollution can occur from on-site sanitation systems, landfills, effluent from wastewater treatment plants, leaking sewers, petrol filling stations or from over application of fertilizers in agriculture. Pollution (or contamination) can also occur from naturally occurring contaminants, such as arsenic or fluoride.[73] Using polluted groundwater causes hazards to public health through poisoning or the spread of disease (water-borne diseases).

The pollutant often creates a contaminant plume within an aquifer. Movement of water and dispersion within the aquifer spreads the pollutant over a wider area. Its advancing boundary, often called a plume edge, can intersect with groundwater wells and surface water, such as seeps and springs, making the water supplies unsafe for humans and wildlife. The movement of the plume, called a plume front, may be analyzed through a hydrological transport model or groundwater model. Analysis of groundwater pollution may focus on soil characteristics and site geology, hydrogeology, hydrology, and the nature of the contaminants. Different mechanisms have influence on the transport of pollutants, e.g. diffusion, adsorption, precipitation, decay, in the groundwater.

By type of source

Sources of surface water pollution can be grouped into two categories based on their origin: point sources and nonpoint sources.

Point sources

Point source water pollution refers to contaminants that enter a waterway from a single, identifiable source, such as a pipe or ditch. Examples of sources in this category include discharges from a sewage treatment plant, a factory, or a city 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).[74] 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.[75]

Nonpoint sources

Nonpoint source (NPS) pollution refers to diffuse contamination (or pollution) of water or air that does not originate from a single discrete source. This type of pollution is often the cumulative effect of small amounts of contaminants gathered from a large area. It is in contrast to point source pollution which results from a single source. Nonpoint source pollution generally results from land runoff, precipitation, atmospheric deposition, drainage, seepage, or hydrological modification (rainfall and snowmelt) where tracing pollution back to a single source is difficult.[76] Nonpoint source water pollution affects a water body from sources such as polluted runoff from agricultural areas draining into a river, or wind-borne debris blowing out to sea. Nonpoint source air pollution affects air quality, from sources such as smokestacks or car tailpipes. Although these pollutants have originated from a point source, the long-range transport ability and multiple sources of the pollutant make it a nonpoint source of pollution; if the discharges were to occur to a body of water or into the atmosphere at a single location, the pollution would be single-point.


Environmental scientists preparing water autosamplers.

Water pollution may be analyzed through several broad categories of methods: physical, chemical and biological. Some methods may be conducted 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.[77]

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, biochemical oxygen demand (BOD),[78]: 102  chemical oxygen demand (COD),[78]: 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 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 equilibrium with its surroundings. Measurements commonly made on-site and in direct contact with the water source in question include temperature, pH, dissolved oxygen, conductivity, 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 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.[79] Scientists gathering this type of data often employ auto-sampler devices that pump increments of water at either time or discharge intervals.

Biological testing

The use of a biomonitor 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.[80] 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.[81] 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.


Share of water bodies with good water quality in 2020 (a water body is classified as "good" quality if at least 80% of monitoring values meet target quality levels, see also SDG 6, Indicator 6.3.2)

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

By country

For example, water pollution in India and China is wide spread. About 90 percent of the water in the cities of China is polluted.[82]

Control and reduction

View of secondary treatment reactors (activated sludge process) at the Blue Plains Advanced Wastewater Treatment Plant, Washington, D.C., United States. Seen in the distance are the sludge digester building and thermal hydrolysis reactors.

Pollution control philosophy

One aspect of environmental protection are mandatory regulations but they are only part of the solution. Other important tools in pollution control include environmental education, economic instruments, market forces and stricter enforcements.[83] 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).[83] 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.[83]

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.[83]

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).

Sanitation and sewage treatment

Fecal sludge collected from pit latrines is dumped into a river at the Korogocho slum in Nairobi, Kenya.

Municipal wastewater (or sewage) can be treated by centralized sewage treatment plants, decentralized wastewater systems, nature-based solutions[84] or in onsite sewage facilities and septic tanks. For example, waste stabilization ponds are a low cost treatment option for sewage, particularly for regions with warm climates.[1]: 182  UV light (sunlight) can be used to degrade some pollutants in waste stabilization ponds (sewage lagoons).[85] The use of safely managed sanitation services would prevent water pollution caused by lack of access to sanitation.[59]

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.[86] 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.[87]

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,[88] but have implemented partial separation projects and green infrastructure approaches.[89] In some cases municipalities have installed additional CSO storage facilities[90] or expanded sewage treatment capacity.[91]

Industrial wastewater treatment

Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans.[92]: 1412  This applies to industries that generate wastewater with high concentrations of organic matter (e.g. oil and grease), toxic pollutants (e.g. heavy metals, volatile organic compounds) or nutrients such as ammonia.[93]: 180  Some industries install a pre-treatment system to remove some pollutants (e.g., toxic compounds), and then discharge the partially treated wastewater to the municipal sewer system.[94]: 60 

Agricultural wastewater treatment

Anaerobic lagoon for treatment of dairy wastes

Agricultural wastewater treatment is a farm management agenda for controlling pollution from confined animal operations and from surface runoff that may be contaminated by chemicals in fertilizer, pesticides, animal slurry, crop residues or irrigation water. Agricultural wastewater treatment is required for continuous confined animal operations like milk and egg production. It may be performed in plants using mechanized treatment units similar to those used for industrial wastewater. Where land is available for ponds, settling basins and facultative lagoons may have lower operational costs for seasonal use conditions from breeding or harvest cycles.[95]: 6–8  Animal slurries are usually treated by containment in anaerobic lagoons before disposal by spray or trickle application to grassland. Constructed wetlands are sometimes used to facilitate treatment of animal wastes.

Nonpoint source pollution includes sediment runoff, nutrient runoff and pesticides. Point source pollution includes animal wastes, silage liquor, milking parlour (dairy farming) wastes, slaughtering waste, vegetable washing water and firewater. Many farms generate nonpoint source pollution from surface runoff which is not controlled through a treatment plant.

Farmers can install erosion controls to reduce runoff flows and retain soil on their fields.[96][97]: pp. 4-95–4-96  Common techniques include contour plowing, crop mulching, crop rotation, planting perennial crops and installing riparian buffers.[98][97]: pp. 4-95–4-96  Farmers can also develop and implement nutrient management plans to reduce excess application of nutrients[98][97]: pp. 4-37–4-38  and reduce the potential for nutrient pollution. To minimize pesticide impacts, farmers may use Integrated Pest Management (IPM) techniques (which can include biological pest control) to maintain control over pests, reduce reliance on chemical pesticides, and protect water quality.[99]

Management of erosion and sediment control

Silt fence 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.[100] 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.[101]

Erosion caused by deforestation and changes in hydrology (soil loss due to water runoff) also results in loss of sediment and, potentially, water pollution.[102][103]

Control of urban runoff (storm water)

Effective control of urban runoff involves reducing the velocity and flow of storm water, as well as reducing pollutant discharges. Local governments use a variety of storm water management techniques to reduce the effects of urban runoff. These techniques, called best management practices for water pollution (BMPs) in some countries, may focus on water quantity control, while others focus on improving water quality, and some perform both functions.[104]

Pollution prevention practices include low impact development (LID) or green infrastructure techniques - known as Sustainable Drainage Systems (SuDS) in the UK, and Water-Sensitive Urban Design (WSUD) in Australia and the Middle East - such as the installation of green roofs and improved chemical handling (e.g. management of motor fuels & oil, fertilizers and pesticides).[105][106][107] Runoff mitigation systems include infiltration basins, bioretention systems, constructed wetlands, retention basins and similar devices.[108][109]


Some examples for legislation to control water pollution are listed below:

See also


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