Water pollution is the contamination of water bodies
, usually as a result of human activities. Water bodies include for example lake
s and groundwater
. Water pollution results when contaminant
s are introduced into the natural environment. For example, releasing inadequately treated wastewater
into natural water bodies can lead to degradation
of aquatic ecosystems
. In turn, this can lead to public health
problems for people living downstream. They may use the same polluted river water for drinking or bathing or irrigation
. Water pollution is the leading worldwide cause of death and disease, e.g. due to water-borne diseases
Water pollution can be classified as surface water
pollution. Marine pollution
and nutrient pollution
are subsets of water pollution. Sources of water pollution are either point source
s or non-point source
s. Point sources have one identifiable cause of the pollution, such as a storm drain
or a wastewater treatment plant
. Non-point sources are more diffuse, such as agricultural runoff
Pollution is the result of the cumulative effect over time. 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.
The causes of water pollution include a wide range of chemical
s and pathogen
s as well as physical parameters. Contaminants may include organic
substances. Elevated temperatures can also lead to polluted water. A common cause of thermal pollution
is the use of water as a coolant
by power plants
and industrial manufacturers. Elevated water temperatures decrease oxygen levels, which can kill fish and alter food chain
composition, reduce species biodiversity
, and foster invasion by new thermophilic
Water pollution is measured by analysing water samples. Physical, chemical and biological tests can be conducted. Control of water pollution requires appropriate infrastructure
and management plans. The infrastructure may include wastewater treatment plants
. Sewage treatment plants
and industrial wastewater
treatment plants are usually required to protect water bodies from untreated wastewater. Agricultural wastewater treatment
for farms, and erosion control
at construction sites can also help prevent water pollution. Nature-based solutions
are another approach to prevent water pollution.
Effective control of urban runoff includes reducing speed and quantity of flow. In the United States, best management practices for water pollution
include approaches to reduce the quantity of water and improve water quality
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. Natural phenomena
such as volcano
es, algae bloom
, and earthquakes
also cause major changes in water quality and the ecological status of water.
Water pollution is a major global problem. It requires ongoing evaluation
and revision of water resource policy
at all levels (international down to individual aquifers and wells). It has been suggested that water pollution is the leading worldwide cause of death and diseases.
Water pollution accounted for the deaths of 1.8 million people in 2015.
The organization Global Oceanic Environmental Survey (GOES) consider water pollution as one of the main environmental problem
s 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, heart phytoplankton
who produce 70% of oxygen
and remove a large part of carbon dioxide
on earth. The organization proposes a number of measures for fixing the situation, but they should be taken in the next 10 years for being effective.
India and China are two countries with high levels of water pollution. An estimated 580 people in India
die of water pollution related illness (including waterborne diseases
) every day. About 90 percent of the water in the cities of China
is polluted. As of 2007, half a billion Chinese had no access to safe drinking water.
In addition to the acute problems of water pollution in developing countries
, developed countries
also continue to struggle with pollution problems. For example, in a report on water quality
in the United States
in 2009, 44 percent of assessed stream miles, 64 percent of assessed lake acres, and 30 percent of assessed bays
square miles were classified as polluted.
Surface water pollution
Surface water pollution includes pollution of rivers, lakes and oceans. A subset of surface water pollution is marine pollution
One common path of entry by contaminant
s to the sea are rivers. An example is directly discharging sewage and industrial waste into the ocean. Pollution such as this occurs particularly in developing nations. In fact, the 10 largest emitters of oceanic plastic pollution worldwide are, from the most to the least, China, Indonesia, Philippines, Vietnam, Sri Lanka, Thailand, Egypt, Malaysia, Nigeria, and Bangladesh, largely through the rivers Yangtze, Indus, Yellow, Hai, Nile, Ganges, Pearl, Amur, Niger, and the Mekong, and accounting for "90 percent of all the plastic that reaches the world's oceans."
es) in the oceans trap floating plastic debris
. Plastic debris can absorb toxic chemicals from ocean pollution, potentially poisoning any creature that eats it. Many of these long-lasting pieces end up in the stomachs of marine birds and animals. This results in obstruction of digestive pathways, which leads to reduced appetite or even starvation.
There are a variety of secondary effects stemming not from the original pollutant, but a derivative condition. An example is silt
-bearing surface runoff
, which can inhibit the penetration of sunlight through the water column, hampering photosynthesis
in aquatic plants.
Interactions between groundwater
and surface water
are complex. Consequently, groundwater pollution, also referred to as groundwater contamination, is not as easily classified as surface water pollution.
By its very nature, groundwater aquifer
s are susceptible to contamination from sources that may not directly affect surface water bodies. The distinction of point vs. non-point source may be irrelevant in some situations.
Analysis of groundwater contamination may focus on soil
characteristics and site geology, hydrogeology
, and the nature of the contaminants. Causes of groundwater pollution include: naturally-occurring (geogenic), on-site sanitation
, commercial and industrial leaks, hydraulic fracturing
, landfill leachate
Categories of pollution sources
Surface water and groundwater
have often been studied and managed as separate resources even though they are interrelated.
Surface water seeps through the soil and becomes groundwater. Conversely, groundwater can also feed surface water sources. Sources of surface water pollution are generally grouped into two categories based on their origin.
Point source water pollution
refers to contaminants that enter a waterway from a single, identifiable source, such as a pipe
. 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. 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 source pollution
refers to diffuse contamination 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. A common example is the leaching out of nitrogen
compounds from fertilized agricultural lands.
in storm water
from "sheet flow" over an agricultural field
or a forest are also cited as examples of non-point source pollution.
Contaminated storm water washed off of parking lot
s, roads and highways, called urban runoff
, is sometimes included under the category of non-point sources. This runoff becomes a point source because it is typically channeled into storm drain systems and discharged through pipes to local surface waters.
Contaminants and their sources
The specific contaminants leading to pollution in water include a wide spectrum of chemical
s, and physical changes such as elevated temperature and discoloration. While many of the chemicals and substances that are regulated may be naturally occurring (calcium
, 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.
-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 gill
s of some fish species.
"Protecting Water Quality from Agricultural Runoff."
Fact Sheet No. EPA-841-F-05-001. March 2005.
Alteration of water's physical chemistry includes acidity (change in pH
), electrical conductivity
, temperature, and eutrophication
. 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.
s are referred to as pathogen
s. Pathogens can produce waterborne diseases
in either human or animal hosts. Coliform bacteria
, which are not an actual cause of disease, are commonly used as a bacterial indicator
of water pollution. Other microorganisms sometimes found in contaminated surface waters that have caused human health problems include:
* ''Burkholderia pseudomallei
* ''Cryptosporidium parvum
* ''Giardia lamblia
'' and other viruses
* ''Parasitic worms
including the Schistosoma
High levels of pathogens may result from on-site sanitation
systems (septic tank
s, pit latrine
s) or inadequately treated sewage
discharges. Older cities with ageing infrastructure may have leaky sewage collection systems (pipes, pumps, valves), which can cause sanitary sewer overflow
s. Some cities also have combined sewer
s, which may discharge untreated sewage during rain storms.
Report to Congress: Impacts and Control of CSOs and SSOs."
August 2004. Document No. EPA-833-R-04-001.
) from sewage
discharges also pollutes water bodies.
Pathogen discharges may also be caused by poorly managed livestock operations.
Organic, inorganic and macroscopic contaminants
Contaminants may include organic
substances. Many of the chemical substances are toxic
Organic water pollutants include:
* Disinfection by-product
s found in chemically disinfected drinking water
, such as chloroform
* Food processing
waste, which can include oxygen-demanding substances, fats and grease
s and herbicide
s, a huge range of organohalide
s and other chemical compounds
hydrocarbons, including fuels (gasoline
, diesel fuel
, jet fuels, and fuel oil
) and lubricants (motor oil), and fuel combustion
byproducts, from storm water runoff
[ Chapter 2.]
* Volatile organic compounds
, such as industrial solvent
s, from improper storage.
* Chlorinated solvent
s, 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
* Various chemical compounds found in personal hygiene
* Drug pollution
involving pharmaceutical drug
s and their metabolites
, this can include antidepressant
drugs or hormonal medicines such as contraceptive pills
. These molecule
s can be small and difficult for treatment plants to remove without expensive upgrades.
Inorganic water pollutants include:
caused by industrial discharges (especially sulfur dioxide
from power plants
from food processing waste
* Chemical waste
as industrial by-products
s containing nutrients--nitrates
s—which are found in storm water runoff from agriculture, as well as commercial and residential use
(see nutrient pollution
* Heavy metals
from motor vehicle
s (via urban storm water runoff
and acid mine drainage
* Secretion of creosote preservative into the aquatic ecosystem
) in runoff from construction sites, logging, slash and burn
practices or land clearing sites.
Macroscopic pollution – large visible items polluting the water – may be termed "floatables" in an urban storm water context, or marine debris
when found on the open seas, and can include such items as:
or garbage (e.g. paper, plastic, or food waste
) discarded by people on the ground, along with accidental or intentional dumping of rubbish, that are washed by rainfall into storm drain
s and eventually discharged into surface waters.
, small ubiquitous waterborne plastic pellets. ''See'' plastic pollution
s, large derelict ships.
Change in 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. Elevated water temperatures decrease oxygen levels, which can kill fish and alter food chain
composition, reduce species biodiversity
, and foster invasion by new thermophilic
Urban runoff may also elevate temperature in surface waters.
Thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers.
Water pollution may be analyzed through several broad categories of methods: physical, chemical and biological. Most involve collection of samples, followed by specialized analytical tests. Some methods may be conducted ''in situ
'', without sampling, such as temperature. Government agencies and research organizations have published standardized, validated analytical test methods to facilitate the comparability of results from disparate testing events.
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. 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
Sampling for biological testing involves collection of plants and animals from the surface water body. Depending on the type of assessment, the organisms may be identified for biosurvey
s (population counts) and returned to the water body, or they may be dissected for bioassay
s to determine toxicity
Common physical tests of water include temperature, solids concentrations (e.g., total suspended solids
(TSS)) and turbidity.
Water samples may be examined using the principles of analytical chemistry
. Many published test methods are available for both organic and inorganic compounds. Frequently used methods include pH
, biochemical oxygen demand
chemical oxygen demand
compounds), metals (including copper, zinc
, lead and mercury
), oil and grease, total petroleum
hydrocarbons (TPH), and pesticide
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 copepod
s and other small water crustacean
s that are present in many water bodies. Such organisms can be monitored for changes (biochemical, physiological, or behavioral) that may indicate a problem within their ecosystem.
Control of pollution
Municipal wastewater treatment
In urban areas of developed countries, municipal wastewater
) is typically treated by centralized sewage treatment plants
. Well-designed and operated systems (i.e., with secondary treatment steps or more advanced treatment) can remove 90 percent or more of the pollutant load in sewage. Some plants have additional systems to remove nutrient
s and pathogens, but these more advanced treatment steps get progressively more expensive.
are also being used instead of (or in combination with) centralized treatment plants.
World Water Development Report 2018: Nature-based Solutions for Water
Cities with sanitary sewer overflow
s or combined sewer overflows
employ one or more engineering
approaches to reduce discharges of untreated sewage, including:
* utilizing a green infrastructure
approach to improve storm water management capacity throughout the system, and reduce the hydraulic
overloading of the treatment plant
* repair and replacement of leaking and malfunctioning equipment
* increasing overall hydraulic capacity of the sewage collection system (often a very expensive option).
On-site sanitation and safely managed sanitation
Households or businesses not served by a municipal treatment plant may have an individual septic tank
, which pre-treats the wastewater on site and infiltrates it into the soil. Improperly designed or installed septic systems can cause groundwater pollution
Globally, about 4.5 billion people do not have safely managed sanitation
as of 2017, according to an estimate by the Joint Monitoring Programme for Water Supply and Sanitation
[WHO and UNICEF (2017]
Progress on Drinking Water, Sanitation and Hygiene: 2017 Update and SDG Baselines
Geneva: World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF), 2017
Lack of access to sanitation 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. The use of safely managed sanitation services would prevent this type of water pollution.
Industrial wastewater treatment
Some industrial facilities generate wastewater that is similar to domestic sewage and can be treated by sewage treatment plants. 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, need specialized treatment systems. 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. Industries generating large volumes of wastewater typically operate their own treatment systems. Some industries have been successful at redesigning their manufacturing processes to reduce or eliminate pollutants, through a process called pollution prevention
To remove heat from wastewater generated by power plants
or manufacturing plants
the following technologies are used:
s, man-made bodies of water designed for cooling by evaporation
, and radiation
s, which transfer waste heat
to the atmosphere
or heat transfer
, a process where waste heat is recycled for domestic or industrial heating purposes.
Agricultural wastewater treatment
Regarding non-point sources, sediment
) washed off fields is the largest source of agricultural pollution
in the United States.
Farmers may utilize erosion control
s to reduce runoff flows and retain soil on their fields. Common techniques include contour plowing
, crop mulch
ing, crop rotation
, planting perennial
crops and installing riparian buffer
[U.S. Natural Resources Conservation Service (NRCS). Washington, DC.]
"National Conservation Practice Standards."
National Handbook of Conservation Practices. Accessed 2015-10-02.
) are typically applied to farmland as commercial fertilizer
, animal manure
, or spraying of municipal or industrial wastewater (effluent) or sludge. Nutrients may also enter runoff from crop residue
, and atmospheric deposition
Farmers can 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.
Farms with large livestock and poultry operations, such as factory farm
s, are often point source dischargers. These facilities are called "concentrated animal feeding operations" or "feedlots" in the US and are being subject to increasing government regulation. Animal slurries
are usually treated by containment in anaerobic lagoon
s before disposal by spray or trickle application to grassland. Constructed wetland
s are sometimes used to facilitate treatment of animal wastes. Some animal slurries are treated by mixing with straw
at high temperature to produce a bacteriologically sterile and friable manure for soil improvement.
Erosion and sediment control from construction sites
Sediment from construction sites is managed by installation of:
* erosion control
s, such as mulch
ing and hydroseeding
* sediment control
s, such as sediment basin
s and silt fence
Discharge of toxic chemicals such as motor fuels and concrete washout is 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.
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 the U.S., 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
techniques, installation of green roof
s and improved chemical handling (e.g. management of motor fuels & oil, fertilizers and pesticides). Runoff mitigation systems include infiltration basin
systems, constructed wetland
s, retention basin
s and similar devices.
[New Jersey Department of Environmental Protection. Trenton, NJ]
"New Jersey Stormwater Best Management Practices Manual."
Thermal pollution from runoff can be controlled by storm water management facilities that absorb the runoff or direct it into groundwater
, such as bioretention systems and infiltration basins. Retention basins tend to be less effective at reducing temperature, as the water may be heated by the sun before being discharged to a receiving stream.
* Aquatic toxicology
* Aspinall and Hick
- landmark water pollution trial, 1880
* Intake fraction
* Trophic state index
(water quality indicator for lakes)
* Water treatment
Water Quality: A Half Century of Progress
a report by the EPA Alumni Association"Troubled Waters"
- video from "Strange Days on Planet Earth" by National Geographic & PBS (US)
– portal for Soil and Water Management in Europe
Causal Analysis/Diagnosis Decision Information System (CADDIS)
- EPA guide for identifying pollution problems; stressor identification
Category:Water and the environment
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