Water pollution

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. 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.

Water pollution can be classified as surface water pollution (for example marine pollution) or groundwater pollution. Sources of water pollution are either point sources or nonpoint sources. Point sources have one identifiable cause, such as a storm drain or a wastewater treatment plant. Nonpoint sources are more diffuse, such as agricultural runoff. Pollution is the result of the cumulative effect over time.

The causes of water pollution include a wide range of chemicals and pathogens as well as physical parameters. 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.

Definition

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". 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.

Impacts

Further information: WASH

Water pollution is a major global problem and can result in the degradation of aquatic ecosystems. 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 water-borne diseases).

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.

Water pollution is a type of pollution that is one of the main environmental problems that can present a danger for the existence of life on earth in the next decades. One of the main concerns is that water pollution can damage phytoplankton who produce 70% of oxygen and remove a large part of carbon dioxide on earth.

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.

Prevalence

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.

By type of water affected

Surface water pollution

A polluted river draining an abandoned copper mine on Anglesey

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. Lack of access to sanitation 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

This section is an excerpt from Marine pollution.[edit]

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. It is a combination of chemicals and trash, most of which comes from land sources and is washed or blown into the ocean. This pollution results in damage to the environment, to the health of all organisms, and to economic structures worldwide. 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. 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. Pathways of pollution include direct discharge, land runoff, ship pollution, bilge 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

This section is an excerpt from Nutrient pollution.[edit]

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 (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. 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.

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. 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. 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. These nutrients can eventually end up in aquatic ecosystems and are a contributor to increased eutrophication. When farmers spread their fertilizer, whether it is organic or synthetically made, some of it will leave as runoff and can collect downstream generating cultural eutrophication.

Groundwater pollution

This section is an excerpt from Groundwater pollution.[edit]

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. Groundwater pollution can occur from on-site sanitation systems, landfill leachate, effluent from wastewater treatment plants, leaking sewers, petrol filling stations, hydraulic fracturing (fracking) or from over application of fertilizers in agriculture. Pollution (or contamination) can also occur from naturally occurring contaminants, such as arsenic or fluoride. Using polluted groundwater causes hazards to public health through poisoning or the spread of disease (water-borne diseases).

The pollutant often produces 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.

The interaction of groundwater contamination with surface waters is analyzed by use of hydrology transport models. Interactions between groundwater and surface water are complex. For example, many rivers and lakes are fed by groundwater. This means that damage to groundwater aquifers e.g. by fracking or over abstraction, could therefore affect the rivers and lakes that rely on it. Saltwater intrusion into coastal aquifers is an example of such interactions. Prevention methods include: applying the precautionary principle, groundwater quality monitoring, land zoning for groundwater protection, locating on-site sanitation systems correctly and applying legislation. When pollution has occurred, management approaches include point-of-use water treatment, groundwater remediation, or as a last resort, abandonment.

By type of source

Characteristics of point and nonpoint sources of chemical inputs (modified from Novonty and Olem 1994)

Point sources Wastewater effluent (municipal and industrial) Runoff and leachate from waste disposal systems Runoff and infiltration from animal feedlots Runoff from mines, oil fields, unsewered industrial sites Overflows of combined storm and sanitary sewers Runoff from construction sites less than 20,000 m2 (220,000 ft²) Untreated sewage Nonpoint sources Runoff from agriculture due to fertilizers and pesticides /irrigation Runoff from pasture and range Urban runoff from unsewered areas Septic tank leachate Runoff from construction sites >20,000 m2 (220,000 ft²) Runoff from abandoned mines Atmospheric deposition over a water surface Other land activities generating contaminants

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). 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.

Nonpoint sources

This section is an excerpt from Nonpoint source pollution.[edit]

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. 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.

Nonpoint source water pollution may derive from many different sources with no specific solutions or changes to rectify the problem, making it difficult to regulate. Nonpoint source water pollution is difficult to control because it comes from the everyday activities of many different people, such as lawn fertilization, applying pesticides, road construction or building construction. Controlling nonpoint source pollution requires improving the management of urban and suburban areas, agricultural operations, forestry operations and marinas.

Types of nonpoint source water pollution include sediment, nutrients, toxic contaminants and chemicals and pathogens. Principal sources of nonpoint source water pollution include: urban and suburban areas, agricultural operations, atmospheric inputs, highway runoff, forestry and mining operations, marinas and boating activities. In urban areas, contaminated storm water washed off of parking lots, roads and highways, called urban runoff, is usually included under the category of non-point sources (it can become a point source if it is channeled into storm drain systems and discharged through pipes to local surface waters). In agriculture, the leaching out of nitrogen compounds from fertilized agricultural lands is a nonpoint source water pollution. Nutrient runoff in storm water from "sheet flow" over an agricultural field or a forest are also examples of non-point source pollution.

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.

Pollutants and their effects (sources of these pollutants are municipal and industrial wastewater, urban runoff, agricultural and pasture activities). Adapted from

Pollutant	Main representative parameter	Possible effect of the pollutant
Suspended solids	Total suspended solids	Aesthetic problems Sludge deposits Pollutants adsorption Protection of pathogens
Biodegradable organic matter	Biological oxygen demand	Oxygen consumption Death of fish Septic conditions
Nutrients	Nitrogen Phosphorus	Excessive algae growth Toxicity to fish (ammonia) Illnesses in new-born infants (Blue baby syndrome from nitrate) Pollution of groundwater
Pathogens	Coliforms, such as E. Coli Helminth eggs	Waterborne diseases
Non-biodegradable organic matter	Pesticides Some detergents Others	Toxicity (various) Foam (detergents) Reduction of oxygen transfer (detergents) Non-biodegradability Bad odors (e.g.: phenols)
Inorganic dissolved solids	Total dissolved solids Conductivity	Excessive salinity – harm to plantations (irrigation) Toxicity to plants (some ions) Problems with soil permeability (sodium)

Pathogens from sewage and agriculture

Further information: Waterborne diseases § Diseases by type of pathogen, and Sewage § Pathogens

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. 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).

Pathogens can produce waterborne diseases in either human or animal hosts. 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

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 during storm events and intensive agriculture (poorly managed livestock operations).

Muddy river polluted by sediment.

Organic contaminants

Contaminants may include organic and inorganic substances. Many of the chemical substances are toxic.

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

Organic water pollutants include:

• Detergents
• Disinfection by-products found in chemically disinfected drinking water, such as chloroform
• Food processing waste, which can include oxygen-demanding substances, such as fats and grease
• Insecticides and herbicides and other chemical compounds
• 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
• Volatile organic compounds, such as industrial solvents, from improper storage.
• Chlorinated solvents, which are dense non-aqueous phase liquids, may fall to the bottom of reservoirs, since they don't mix well with water and are denser.
  • Polychlorinated biphenyl (PCBs)
  • Trichloroethylene
• Perchlorate
• Various chemical compounds found in personal hygiene and cosmetic products which are disposed of in domestic wastewater and then discharged from sewage treatment plants
• Drug pollution involving illicit drugs, pharmaceutical drugs and their metabolites, again from wastewater (see also wastewater epidemiology). This can include antidepressant drugs or hormonal medicines such as the contraceptive pill.

Inorganic contaminants

Inorganic water pollutants include:

• Acidity caused by industrial discharges (especially sulfur dioxide from power plants). In industrialized areas rain can be acidic because of dissolved oxides of sulfur and nitrogen formed from burning of fossil fuels in cars, factories, trains and aircraft and from the atmospheric emissions of industry. In some cases this acid rain results in pollution of lakes and rivers.
• Ammonia from food processing waste
• Chemical waste as industrial by-products
• Fertilizers containing nutrients--nitrates and phosphates—which are found in storm water runoff from agriculture, as well as commercial and residential use (see nutrient pollution)
• Heavy metals from motor vehicles (via urban storm water runoff) and acid mine drainage
• Creosote - a chemical used for wood preservation, can be released into the ocean over time
• Silt (sediment) in runoff from construction sites or sewage, logging, slash and burn practices or land clearing sites.

Contaminants from industrial wastewater

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

Solid waste and plastics

Further information: Sewage § Solid waste, and 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 term marine debris is used in the context of pollution of oceans.

This section is an excerpt from Marine debris.[edit]

Marine debris, also known as marine litter, is human-created solid material that has deliberately or accidentally been released in seas or the 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. 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. Waterborne plastic poses a serious threat to fish, seabirds, marine reptiles, and marine mammals, as well as to boats and coasts.

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 discarded fishing nets capturing animals, concentration of plastic debris in massive marine garbage patches, and increasing concentrations of contaminants in the food chain.

This section is an excerpt from Microplastics § Oceans.[edit]

Temperature increase or decrease

The Brayton Point Power Station in Massachusetts discharges heated water to Mount Hope Bay.

This section is an excerpt from Thermal pollution.[edit]

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 drop 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 runoff—stormwater discharged to surface waters from rooftops, roads, and parking lots—and reservoirs can also be a source of thermal pollution. Thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers.

When water used as a coolant is returned to the natural environment at a higher temperature, the sudden change in temperature decreases oxygen supply and affects ecosystem composition. Fish and other organisms adapted to particular temperature range can be killed by an abrupt change in water temperature (either a rapid increase or decrease) known as "thermal shock". Warm coolant water can also have long term effects on water temperature, increasing the overall temperature of water bodies, including deep water. Seasonality effects how these temperature increases are distributed throughout the water column. Elevated water temperatures decrease oxygen levels, which can kill fish and alter food chain composition, reduce species biodiversity, and foster invasion by new thermophilic species.

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.

Others

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

Measurement

Environmental scientists preparing water autosamplers.

Further information: Environmental monitoring, Water chemistry analysis, and Environmental chemistry

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.

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), chemical oxygen demand (COD),, 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.

Sampling

This section is an excerpt from Water quality § sampling.[edit]

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. Scientists gathering this type of data often employ auto-sampler devices that pump increments of water at either time or discharge intervals.

Biological testing

Main article: Bioindicator

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. 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. 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.

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.

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). With regards to groundwater, both fracking and landfill leachate are big issues in water pollution management in the 21st century.

Sanitation and sewage treatment

Further information: Sanitation, WASH, and Water issues in developing countries

Municipal wastewater (or sewage) can be treated by centralized sewage treatment plants, decentralized wastewater systems, nature-based solutions 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. UV light (sunlight) can be used to degrade some pollutants in waste stabilization ponds (sewage lagoons). 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 steps or more advanced tertiary treatment) can remove 90 percent or more of the pollutant load in sewage. 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.

Sewer overflows during storm events can be prevented by timely maintenance and upgrades of the sewerage system. Specifically, mitigation of combined sewer overflows include sewer separation, CSO storage, expanding sewage

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

treatment capacity, retention basins, screening and disinfection facilities, reducing stormwater flows and green infrastructure.

Industrial wastewater treatment

This section is an excerpt from Industrial wastewater treatment.[edit]

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. 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. 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.

Agricultural wastewater treatment

This section is an excerpt from Agricultural wastewater treatment.[edit]

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. 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. Common techniques include contour plowing, crop mulching, crop rotation, planting perennial crops and installing riparian buffers. Farmers can also develop and implement nutrient management plans to reduce excess application of nutrients 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.

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. 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.

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

Control of urban runoff (storm water)

This section is an excerpt from Urban runoff § Prevention and mitigation.[edit]

Effective control of urban runoff involves reducing the velocity and flow of stormwater, as well as reducing pollutant discharges. Local governments use a variety of stormwater 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.

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, pesticides and roadway deicers). Runoff mitigation systems include infiltration basins, bioretention systems, constructed wetlands, retention basins, and similar devices.

Legislation

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

• In the Philippines, Republic Act 9275, otherwise known as the Philippine Clean Water Act of 2004, 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.
• The Clean Water Act is the primary federal law in the United States governing water pollution in surface waters. It is implemented by the U.S. Environmental Protection Agency in collaboration with states, territories, and tribes. Groundwater protection provisions are included in the Safe Drinking Water Act, Resource Conservation and Recovery Act, and the Superfund act.

See also

• Aquatic toxicology
• Environmental impact of pesticides § Water
• Pollution
• Trophic state index (water quality indicator for lakes)
• Water treatment
• Water resources management

External links

• Causal Analysis/Diagnosis Decision Information System (CADDIS) - EPA guide for identifying pollution problems; stressor identification