fresh, coastal, and ocean waters. the specific contaminants leading to pollution in water include a wide spectrum of chemicals, pathogens, and physical changes such as elevated temperature. while many of the chemicals and substances that are regulated may be naturally occurring (calcium, sodium, iron, manganese, etc.) the concentration usually determines what is a natural component of water and what is a contaminant. high concentrations of naturally occurring substances can have negative impacts on aquatic flora and fauna. oxygen-depleting substances may be natural materials such as plant matter (e.g. leaves and grass) as well as 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.fecal sludge collected from pit latrines is dumped into a river at the korogocho slum in nairobi, kenya. public health and waterborne diseases further information: wash § health aspects a study published in 2017 stated that "polluted water spread gastrointestinal diseases and parasitic infections and killed 1.8 million people" (these are also referred to as waterborne diseases). persistent exposure to pollutants through water are environmental health hazards, which can increase the likelihood for one to develop cancer or other diseases. eutrophication from nitrogen pollution nitrogen pollution can cause eutrophication, especially in lakes. eutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases the primary productivity of the ecosystem. subsequent negative environmental effects such as anoxia (oxygen depletion) and severe reductions in water quality may occur.: 131 this can harm fish and other animal populations. this section is an excerpt from eutrophication. eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. it has also been defined as "nutrient-induced increase in phytoplankton productivity".: 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. eutrophication can affect freshwater or salt water systems. in freshwater ecosystems it is almost always caused by excess phosphorus. in coastal waters on the other hand, the main contributing nutrient is more likely to be nitrogen, or nitrogen and phosphorus together. this depends on the location and other factors. 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 (co2) from the atmosphere. 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.water pollution by countryafghanistanalbaniaalgeriaaustraliabangladeshbelgiumbrazilcanadachilechinacolombiacroatiadenmarkdominican republicegyptel salvadorgeorgiaghanaguatemalahondurasindiaindonesiairanjapankazakhstankenyakuwaitlebanonliberialibyamexicomongolianepalnew zealandnicaraguapakistanparaguayperuphilippinespolandrussiaserbiasingaporesri lankasyriataiwanthailandturkeyugandaunited statesuruguayuzbekistanvenezuelavietnamzimbabwe 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. standards can be "precise" (for a defined quantifiable minimum or maximum value for a pollutant), or "imprecise" which would require the use of best available technology (bat) or best practicable environmental option (bpeo). market-based economic instruments for pollution control can include: charges, subsidies, deposit or refund schemes, the creation of a market in pollution credits, and enforcement incentives. moving towards a holistic approach in chemical pollution control combines the following approaches: integrated control measures, trans-boundary considerations, complementary and supplementary control measures, life-cycle considerations, the impacts of chemical mixtures. control of water pollution requires appropriate infrastructure and management plans. the infrastructure may include wastewater treatment plants, for example sewage treatment plants and industrial wastewater treatment plants. agricultural wastewater treatment for farms, and erosion control at construction sites can also help prevent water pollution. effective control of urban runoff includes reducing speed and quantity of flow. water pollution requires ongoing evaluation and revision of water resource policy at all levels (international down to individual aquifers and wells). sanitation and sewage treatment further information: sanitation, wash, and water issues in developing countries plastic waste on the big drainage, and air pollution in the far end of the drainage in ghana municipal wastewater 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.: 182 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 stages 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 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, but have implemented partial separation projects and green infrastructure approaches. in some cases municipalities have installed additional cso storage facilities or expanded sewage treatment capacity. industrial wastewater treatment this section is an excerpt from 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.: 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.: 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.: 60 agricultural wastewater treatment this section is an excerpt from agricultural wastewater treatment. 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.: 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. 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. 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. 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. philippines 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. united states this section is an excerpt from water pollution in the united states § current regulations. the clean water act is the primary federal law in the united states governing water pollution in surface waters. the 1972 cwa amendments established a broad regulatory framework for improving water quality. the law defines procedures for pollution control and developing criteria and standards for pollutants in surface water. the law authorizes the environmental protection agency to regulate surface water pollution in the united states, in partnership with state agencies. prior to 1972 it was legal to discharge wastewater to surface waters without testing for or removing water pollutants. the cwa was amended in 1981 and 1987 to adjust the federal proportion of construction grant funding for local governments, regulate municipal storm sewer discharges and to later establish the clean water state revolving fund. the fund provides low-interest loans to improve municipal sewage treatment systems and finance other water quality improvements.