water body (river, lakes, sea) or land, its relative impact will depend on the assimilative capacity of the water body or ecosystem.: 78 water bodies have a self-purification capacity, so that the concentration of a pollutant may decrease along the distance from the discharge point. furthermore, water bodies provide a dilution to the pollutants concentrations discharged, although it does not decrease their mass. in principle, the higher the dilution capacity (ratio of volume or flow of the receiving water and volume or flow of sewage discharged), the lower will be the concentration of pollutants in the receiving water, and probably the lower will be the negative impacts. but if the water body already arrives very polluted at the point of discharge, the dilution will be of limited value. in several cases, a community may treat partially its sewage, and still count on the assimilative capacity of the water body. however, this needs to be analyzed very carefully, taking into account the quality of the water in the receiving body before it receives the discharge of sewage, the resulting water quality after the discharge and the impact on the intended water uses after discharge. there are also specific legal requirements in each country. different countries have different regulations regarding the specifications of the quality of the sewage being discharged and the quality to be maintained in the receiving water body.: 152 the combination of treatment and disposal must comply with existing local regulations. the assimilative capacity depends – among several factors – on the ability of the receiving water to sustain dissolved oxygen concentrations necessary to support organisms catabolizing organic waste.: 9, 673 for example, fish may die if dissolved oxygen levels are depressed below 5 mg/l.: 573 application of sewage to land can be considered as a form of final disposal or of treatment, or both.: 189 land disposal alternatives require consideration of land availability, groundwater quality, and possible soil deterioration. other disposal methods sewage may be discharged to an evaporation or infiltration basin..: 9–41 groundwater recharge is used to reduce saltwater intrusion, or replenish aquifers used for agricultural irrigation. treatment is usually required to sustain percolation capacity of infiltration basins, and more extensive treatment may be required for aquifers used as drinking water supplies.: 700–703 marine outfall this section is an excerpt from marine outfall. a marine outfall (or ocean outfall) is a pipeline or tunnel that discharges municipal or industrial wastewater, stormwater, combined sewer overflows (csos), cooling water, or brine effluents from water desalination plants to the sea. usually they discharge under the sea's surface (submarine outfall). in the case of municipal wastewater, effluent is often being discharged after having undergone no or only primary treatment, with the intention of using the assimilative capacity of the sea for further treatment. submarine outfalls are common throughout the world and probably number in the thousands. the light intensity and salinity in natural sea water disinfects the wastewater to ocean outfall system significantly. more than 200 outfalls alone have been listed in a single international database maintained by the institute for hydromechanics at karlsruhe university for the international association of hydraulic engineering and research (iahr) / international water association (iwa) committee on marine outfall systems. global situation this section is an excerpt from sewage treatment § global situation. before the 20th century in europe, sewers usually discharged into a body of water such as a river, lake, or ocean. there was no treatment, so the breakdown of the human waste was left to the ecosystem. this could lead to satisfactory results if the assimilative capacity of the ecosystem is sufficient which is nowadays not often the case due to increasing population density.: 78 today, the situation in urban areas of industrialized countries is usually that sewers route their contents to a sewage treatment plant rather than directly to a body of water. in many developing countries, however, the bulk of municipal and industrial wastewater is discharged to rivers and the ocean without any treatment or after preliminary treatment or primary treatment only. doing so can lead to water pollution. few reliable figures exist on the share of the wastewater collected in sewers that is being treated in the world. a global estimate by undp and un-habitat in 2010 was that 90% of all wastewater generated is released into the environment untreated. a more recent study in 2021 estimated that globally, about 52% of sewage is treated. however, sewage treatment rates are highly unequal for different countries around the world. for example, while high-income countries treat approximately 74% of their sewage, developing countries treat an average of just 4.2%. as of 2022, without sufficient treatment, more than 80% of all wastewater generated globally is released into the environment. high-income nations treat, on average, 70% of the wastewater they produce, according to un water. only 8% of wastewater produced in low-income nations receives any sort of treatment. treatment main article: sewage treatment sewage treatment is beneficial in reducing environmental pollution. bar screens can remove large solid debris from sewage,: 274–275 and primary treatment can remove floating and settleable matter.: 446 primary treated sewage usually contains less than half of the original solids content and approximately two-thirds of the bod in the form of colloids and dissolved organic compounds. secondary treatment can reduce the bod of organic waste in undiluted sewage,: 575 but is less effective for dilute sewage. water disinfection may be attempted to kill pathogens prior to disposal, and is increasingly effective after more elements of the foregoing treatment sequence have been completed.: 359 reuse and reclamation main article: reclaimed water an alternative to discharge into the environment is to reuse the sewage in a productive way (for agricultural, urban or industrial uses), in compliance with local regulations and requirements for each specific reuse application. public health risks of sewage reuse in agriculture can be minimized by following a "multiple barrier approach" according to guidelines by the world health organization. there is also the possibility of resource recovery which could make agriculture more sustainable by using carbon, nitrogen, phosphorus, water and energy recovered from sewage. sewage farm this section is an excerpt from sewage farm. sewage farms use sewage for irrigation and fertilizing agricultural land. the practice is common in warm, arid climates where irrigation is valuable while sources of fresh water are scarce. suspended solids may be converted to humus by microbes and bacteria in order to supply nitrogen, phosphorus and other plant nutrients for crop growth. many industrialized nations use conventional sewage treatment plants nowadays instead of sewage farms. these reduce vector and odor problems; but sewage farming remains a low-cost option for some developing countries. sewage farming should not be confused with sewage disposal through infiltration basins or subsurface drains. regulations management of sewage includes collection and transport for release into the environment, after a treatment level that is compatible with the local requirements for discharge into water bodies, onto soil or for reuse applications.: 156 in most countries, uncontrolled discharges of wastewater to the environment are not permitted under law, and strict water quality requirements are to be met. for requirements in the united states, see clean water act. sewage management regulations are often part of broader sanitation policies of a country. these may also include the management of human excreta (from non-sewered collection systems), solid waste and stormwater.