Dataset: Environment Database - Wastewater treatment (% population connected)
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Last updated: July 2017

Contact: ENV.Stat@oecd.org

Disclaimer: Data available to the OECD Secretariat by April 2017, and subject to possible slight revisions

This dataset provides information on the level of public equipment installed by countries to managed and abate water pollution. It shows the percentage of national population connected to "public" sewerage networks and related treatment facilities, and the percentage of national population connected to "public" wastewater treatment plants, and the degree of treatment. Connected here means actually connected to a wastewater plants through a public sewage network. Individual private treatment facilities such as septic tanks are not covered here. When analysing these data, it should be kept in mind that the optimal connection rate is not necessarily 100 per cent; it may vary among countries and depends on geographical features and on the spatial distribution of habitats. The interpretation of those data should take into account some variations in countries' definitions, as reflected in metadata.

Austria: Independent treatment and public treatment are estimations based on connection rates to wastewater treatment plants with primary, secondary and tertiary treatment.

Canada: Primary treatment includes preliminary treatment (1%) before 2009. Since 2004 independent wastewater treatment includes private septic systems and private chemical wastewater treatment. In 2004 and 2006, calculations of population connected to sewer systems were based only on municipalities that had sewers. Treatment level data for 2009 and 2006 are not directly comparable due to changes in survey methodology. The definition of tertiary treatment was changed for the 2009 survey to bring it into alignment with updated federal municipal wastewater regulations. Before 2009, a plant could be considered to have tertiary treatment if it included primary treatment with nutrient removal. In 2009, this definition was changed to have tertiary treatment as a physical process added to secondary treatment. This change in definition meant that many plants that had previously been counted as tertiary plants were counted as secondary treatment plants in 2009. Plants with preliminary treatment are, as of 2009, grouped in the no-treatment category. This change has a very small effect on the "without treatment" category

Chile: Data refer only to population living in urban areas served by sanitary companies. Data is therefore not comparable with other countries. Primary treatment includes primary treatment with disinfection and submarine emissaries. Secondary treatment includes aerated lagoons. Tertiary treatment includes activated sludge (because this system has a disinfection phase to meet the standard of 1000FC/100ml, but it doesn´t have nutrients treatment).

Czech Republic: For more information see http://eagri.cz/public/web/en/mze/water/water-management/

Denmark: Independent treatment figures are based on data for scattered settlements, where wastewater is treated either mechanically or biologically

Estonia: For more information , see www.keskkonnaagentuur.ee

France: Data is based on a 2008 survey which has not been updated. Calculations for treatment types are based on the maximum entry load in population equivalents. For each year, starting in 2010, the percentage by treatment type is estimated assuming a constant total of 82%, estimated in 2008, of the population connected to public sewage. For more d'information see http://assainissement.developpement-durable.gouv.fr/services.php

Germany: Before 1991 data refer to western Germany only. Unspecified treatment refers to population connected to industrial or foreign wastewater treatment plants or cesspits (total public sewerage and public total treatment include population whose wastewater is transported from independent storage tanks to wastewater treatment plants by means of trucks)

Greece: Data refer to agglomerations with more than 2000 population equivalent

Iceland: Primary treatment includes 3.2% of preliminary treatment

Ireland: 2015 data: (a) the 46.84% that receives secondary treatment includes 28.52% that also received UV disinfection for at least some part of the year; (b) the 2.87% listed as public sewage network without treatment in 2015 includes 1.42% that received basic preliminary treatment (e.g. screening to remove rags and large solids) prior to discharge; (c) the 3.03% not benefitting from any sewage treatment includes the 2.87% that is collected in public sewers but received no treatment. Public sewage network without treatment in 2013 and 2014 includes approximately 1.6% that received preliminary treatment prior to discharge (e.g. screening to remove rags and large solids). Secondary treatment in 2013 and 2014 includes approximately 27% that also received UV disinfection for at least some part of the year. The percentage of the population served by independent treatment (e.g. single houses served by on-site treatment systems such as septic tanks) from 2011 to 2015 was obtained from the 2011 census data, available on http://www.cso.ie/.  The percentage of the population served by independent treatment is unlikely to change significantly from year to year and therefore the 2011 census data is considered the best estimate to use for 2011 to 2015.  From 2011 the data on wastewater treated in the public sewage system is based on the type of treatment provided (by population equivalent, p.e.) at all agglomerations subject to the Environmental Protection Agency's waste water discharge licensing programme (i.e.> 500 p.e.). The 2009 figure for population connected to public sewage treatment appears to be overestimated, due to a corresponding underestimation in population connected to independent treatment. The 1999 and 2001 data appears to exclude the population connected to independent treatment (e.g. on-site waste water treatment plants such as septic tanks). Data before 1999 excludes some agglomerations of less than 2,000 p.e. Investment in wastewater infrastructure has brought considerable improvements in the provision of treatment of wastewater collected in the public sewage network since 2001. For more information see http://www.epa.ie/ ; http://www.epa.ie/pubs/reports/water/wastewater/ ; http://www.cso.ie/ and

http://www.cso.ie/en/census/census2011reports/census2011profile4theroofoverourheads-housinginireland.

The Environmental Protection Agency publishes a comprehensive national report on urban waste water treatment in Ireland each year and these reports are available on the Environmental Protection Agency's website at http://www.epa.ie/pubs/reports/water/wastewater

Italy: The figure for the population connected to public sewerage is overestimated because it is assumed that the public sewerage supplies the entire municipal population and the figure is calculated using population equivalence (data refer to sewage treatment plants serving agglomerations of more than 2000 population equivalent).

Japan: Secondary treatment in 1980 may include data for primary and tertiary treatment. 2010-2015 data does not include some municipalities that were unable to carry out a survey because of an earthquake. For more information: http://www.mlit.go.jp/ (Ministry of Land, Infrastructure, Transport and Tourism)

Korea: There is no official information on independent treatment. It is estimated here as 100% minus total public sewerage. The large increase of tertiary treatment between 2012 and 2013 is due to the entering into force and the implementation of a regulation on public sewage. For more information see: Korea Statistical Information service (http://kosis.kr/) and Environmental Statistic Information System (http://stat.me.go.kr/).

Latvia: The population using independent treatment is computed as the difference between the total population and the number of inhabitants who reported, in surveys by water using operators, to be connected to treatment plants. In agglomerations with population equivalent of more than 2000 the percentage of population connected to the centralised sewerage system is increasing and, as a result, the percentage benefitting from independent treatment is decreasing in the last years. The main areas for investment in 2014 - 2020 are the extension and rehabilitation of water and wastewater networks in agglomerations with population equivalent of more than 10000 and in agglomerations with population equivalent 2000 - 10000 where network coverage is below 100%. Increasing household connections to centralised systems is one of the main challenges to which the country is confronted. Further information can be found in http://www.meteo.lv/fs/CKFinderJava/userfiles/files/Vide/Udens/notekudeni/2014_

ZINOJUMS_NOTEKUD_PARSKATS.pdf

Mexico: There is no official information about population connected to wastewater treatment plants. Estimates are based on treated wastewater. For more information: http://www.conagua.gob.mx,

http://www.gob.mx/semarnat/acciones-y-programas/sistema-nacional-de-informacion-ambiental-y-de-recursos-naturales

New Zealand: 2014 data and older: data is based on the total of reported populations for the areas served by individual treatment plants, as used in New Zealand's greenhouse gas inventory. This is likely to be a low-end estimate (uncertainty from 0 to +6%) as the total known to have public connections or septic tanks is 94% (independent treatment in the last available year is estimated as 94% less total treatment), leaving 6% of the population unaccounted for. There has been a very slow increase in the estimated percentage of population connected to public sewer systems, due to urban population growth. 2015 data: estimations based on data for 85% of the population. Data by type of treatment is not available because standards are set at the local level and there is no uniformity across the country. For more information see http://www.waternz.org.nz/WWTPInventory and http://www.stats.govt.nz/.

Norway: Primary treatment: wastewater treatment plants (serving 50 population equivalent - p.e. - or more) with natural purification, mechanical or other treatment.  Secondary treatment: wastewater treatment plants (serving 50 p.e. or more) with biological treatment. Tertiary treatment: wastewater treatment plants (serving 50 pe or more) with chemical or chemical + biological treatment. Further information:

https://www.ssb.no/en/avlut et http://www.ssb.no/natur-og-miljo/artikler-og-publikasjoner/kommunale-avlop

Slovak Republic: For more information see http://www.enviroportal.sk/indicator/detail?id=1784

http://www.enviroportal.sk/indicator/detail?id=1349

https://www.enviroportal.sk/spravy/index

Spain: Data only refers to urban agglomerations of more than 2,000 population equivalent (p.e., approximately 1,300 inhabitants). For agglomerations of less than 2,000 p.e. data include estimates. Systems of septic tanks are included in urban wastewater treatment

Sweden: Primary treatment may include removal of sediments. Based on register studies on wastewater conditions in rural areas, it is assumed that everybody living in urban areas is connected to a wastewater treatment plant. Secondary and tertiary treatment data: estimation based on a technical survey for the reporting year 2010 on the population connected to UWWTP. Industrial facilities with own treatment plants are excluded from this estimation. A technical survey indicated that around 60% of the people connected to independent facilities had secondary treatment. For more information: http://www.scb.se/

Turkey: Break in series in 2010. Before 2010 data referred only to municipalities, after 2010 also to rural areas

United States: Primary treatment may include ocean outfalls and some biological treatment. Tertiary treatment includes 2-3% of non-discharge treatment, e.g. lagoons, evaporation ponds. Exclude rural areas served by Onsite Disposal Systems

England and Wales: Data refer to the financial year (April to March) until 2000. Independent treatment in 2012 is estimated by assuming that there are 2 persons per property. Data for 2014 refers to England only.

Costa Rica: Data are estimates. Data by type of treatment are not available: the volumes of wastewater are estimated using a coefficient of return of 70%, on the basis of which other data are inferred. In addition, it is common to use the sewage to evacuate storm water, which would cause measurement bias. For more information see http://www.inec.go.cr/

Dataset: Environment Database - Wastewater treatment (% population connected)Contact person/organisation
ENV.Stat@oecd.org
Unit of measure usedPercentagePower codeUnitsKey statistical concept

Last updated: July 2017

Contact: ENV.Stat@oecd.org

Disclaimer: Data available to the OECD Secretariat by April 2017, and subject to possible slight revisions

This dataset provides information on the level of public equipment installed by countries to managed and abate water pollution. It shows the percentage of national population connected to "public" sewerage networks and related treatment facilities, and the percentage of national population connected to "public" wastewater treatment plants, and the degree of treatment. Connected here means actually connected to a wastewater plants through a public sewage network. Individual private treatment facilities such as septic tanks are not covered here. When analysing these data, it should be kept in mind that the optimal connection rate is not necessarily 100 per cent; it may vary among countries and depends on geographical features and on the spatial distribution of habitats. The interpretation of those data should take into account some variations in countries' definitions, as reflected in metadata.

Austria: Independent treatment and public treatment are estimations based on connection rates to wastewater treatment plants with primary, secondary and tertiary treatment.

Canada: Primary treatment includes preliminary treatment (1%) before 2009. Since 2004 independent wastewater treatment includes private septic systems and private chemical wastewater treatment. In 2004 and 2006, calculations of population connected to sewer systems were based only on municipalities that had sewers. Treatment level data for 2009 and 2006 are not directly comparable due to changes in survey methodology. The definition of tertiary treatment was changed for the 2009 survey to bring it into alignment with updated federal municipal wastewater regulations. Before 2009, a plant could be considered to have tertiary treatment if it included primary treatment with nutrient removal. In 2009, this definition was changed to have tertiary treatment as a physical process added to secondary treatment. This change in definition meant that many plants that had previously been counted as tertiary plants were counted as secondary treatment plants in 2009. Plants with preliminary treatment are, as of 2009, grouped in the no-treatment category. This change has a very small effect on the "without treatment" category

Chile: Data refer only to population living in urban areas served by sanitary companies. Data is therefore not comparable with other countries. Primary treatment includes primary treatment with disinfection and submarine emissaries. Secondary treatment includes aerated lagoons. Tertiary treatment includes activated sludge (because this system has a disinfection phase to meet the standard of 1000FC/100ml, but it doesn´t have nutrients treatment).

Czech Republic: For more information see http://eagri.cz/public/web/en/mze/water/water-management/

Denmark: Independent treatment figures are based on data for scattered settlements, where wastewater is treated either mechanically or biologically

Estonia: For more information , see www.keskkonnaagentuur.ee

France: Data is based on a 2008 survey which has not been updated. Calculations for treatment types are based on the maximum entry load in population equivalents. For each year, starting in 2010, the percentage by treatment type is estimated assuming a constant total of 82%, estimated in 2008, of the population connected to public sewage. For more d'information see http://assainissement.developpement-durable.gouv.fr/services.php

Germany: Before 1991 data refer to western Germany only. Unspecified treatment refers to population connected to industrial or foreign wastewater treatment plants or cesspits (total public sewerage and public total treatment include population whose wastewater is transported from independent storage tanks to wastewater treatment plants by means of trucks)

Greece: Data refer to agglomerations with more than 2000 population equivalent

Iceland: Primary treatment includes 3.2% of preliminary treatment

Ireland: 2015 data: (a) the 46.84% that receives secondary treatment includes 28.52% that also received UV disinfection for at least some part of the year; (b) the 2.87% listed as public sewage network without treatment in 2015 includes 1.42% that received basic preliminary treatment (e.g. screening to remove rags and large solids) prior to discharge; (c) the 3.03% not benefitting from any sewage treatment includes the 2.87% that is collected in public sewers but received no treatment. Public sewage network without treatment in 2013 and 2014 includes approximately 1.6% that received preliminary treatment prior to discharge (e.g. screening to remove rags and large solids). Secondary treatment in 2013 and 2014 includes approximately 27% that also received UV disinfection for at least some part of the year. The percentage of the population served by independent treatment (e.g. single houses served by on-site treatment systems such as septic tanks) from 2011 to 2015 was obtained from the 2011 census data, available on http://www.cso.ie/.  The percentage of the population served by independent treatment is unlikely to change significantly from year to year and therefore the 2011 census data is considered the best estimate to use for 2011 to 2015.  From 2011 the data on wastewater treated in the public sewage system is based on the type of treatment provided (by population equivalent, p.e.) at all agglomerations subject to the Environmental Protection Agency's waste water discharge licensing programme (i.e.> 500 p.e.). The 2009 figure for population connected to public sewage treatment appears to be overestimated, due to a corresponding underestimation in population connected to independent treatment. The 1999 and 2001 data appears to exclude the population connected to independent treatment (e.g. on-site waste water treatment plants such as septic tanks). Data before 1999 excludes some agglomerations of less than 2,000 p.e. Investment in wastewater infrastructure has brought considerable improvements in the provision of treatment of wastewater collected in the public sewage network since 2001. For more information see http://www.epa.ie/ ; http://www.epa.ie/pubs/reports/water/wastewater/ ; http://www.cso.ie/ and

http://www.cso.ie/en/census/census2011reports/census2011profile4theroofoverourheads-housinginireland.

The Environmental Protection Agency publishes a comprehensive national report on urban waste water treatment in Ireland each year and these reports are available on the Environmental Protection Agency's website at http://www.epa.ie/pubs/reports/water/wastewater

Italy: The figure for the population connected to public sewerage is overestimated because it is assumed that the public sewerage supplies the entire municipal population and the figure is calculated using population equivalence (data refer to sewage treatment plants serving agglomerations of more than 2000 population equivalent).

Japan: Secondary treatment in 1980 may include data for primary and tertiary treatment. 2010-2015 data does not include some municipalities that were unable to carry out a survey because of an earthquake. For more information: http://www.mlit.go.jp/ (Ministry of Land, Infrastructure, Transport and Tourism)

Korea: There is no official information on independent treatment. It is estimated here as 100% minus total public sewerage. The large increase of tertiary treatment between 2012 and 2013 is due to the entering into force and the implementation of a regulation on public sewage. For more information see: Korea Statistical Information service (http://kosis.kr/) and Environmental Statistic Information System (http://stat.me.go.kr/).

Latvia: The population using independent treatment is computed as the difference between the total population and the number of inhabitants who reported, in surveys by water using operators, to be connected to treatment plants. In agglomerations with population equivalent of more than 2000 the percentage of population connected to the centralised sewerage system is increasing and, as a result, the percentage benefitting from independent treatment is decreasing in the last years. The main areas for investment in 2014 - 2020 are the extension and rehabilitation of water and wastewater networks in agglomerations with population equivalent of more than 10000 and in agglomerations with population equivalent 2000 - 10000 where network coverage is below 100%. Increasing household connections to centralised systems is one of the main challenges to which the country is confronted. Further information can be found in http://www.meteo.lv/fs/CKFinderJava/userfiles/files/Vide/Udens/notekudeni/2014_

ZINOJUMS_NOTEKUD_PARSKATS.pdf

Mexico: There is no official information about population connected to wastewater treatment plants. Estimates are based on treated wastewater. For more information: http://www.conagua.gob.mx,

http://www.gob.mx/semarnat/acciones-y-programas/sistema-nacional-de-informacion-ambiental-y-de-recursos-naturales

New Zealand: 2014 data and older: data is based on the total of reported populations for the areas served by individual treatment plants, as used in New Zealand's greenhouse gas inventory. This is likely to be a low-end estimate (uncertainty from 0 to +6%) as the total known to have public connections or septic tanks is 94% (independent treatment in the last available year is estimated as 94% less total treatment), leaving 6% of the population unaccounted for. There has been a very slow increase in the estimated percentage of population connected to public sewer systems, due to urban population growth. 2015 data: estimations based on data for 85% of the population. Data by type of treatment is not available because standards are set at the local level and there is no uniformity across the country. For more information see http://www.waternz.org.nz/WWTPInventory and http://www.stats.govt.nz/.

Norway: Primary treatment: wastewater treatment plants (serving 50 population equivalent - p.e. - or more) with natural purification, mechanical or other treatment.  Secondary treatment: wastewater treatment plants (serving 50 p.e. or more) with biological treatment. Tertiary treatment: wastewater treatment plants (serving 50 pe or more) with chemical or chemical + biological treatment. Further information:

https://www.ssb.no/en/avlut et http://www.ssb.no/natur-og-miljo/artikler-og-publikasjoner/kommunale-avlop

Slovak Republic: For more information see http://www.enviroportal.sk/indicator/detail?id=1784

http://www.enviroportal.sk/indicator/detail?id=1349

https://www.enviroportal.sk/spravy/index

Spain: Data only refers to urban agglomerations of more than 2,000 population equivalent (p.e., approximately 1,300 inhabitants). For agglomerations of less than 2,000 p.e. data include estimates. Systems of septic tanks are included in urban wastewater treatment

Sweden: Primary treatment may include removal of sediments. Based on register studies on wastewater conditions in rural areas, it is assumed that everybody living in urban areas is connected to a wastewater treatment plant. Secondary and tertiary treatment data: estimation based on a technical survey for the reporting year 2010 on the population connected to UWWTP. Industrial facilities with own treatment plants are excluded from this estimation. A technical survey indicated that around 60% of the people connected to independent facilities had secondary treatment. For more information: http://www.scb.se/

Turkey: Break in series in 2010. Before 2010 data referred only to municipalities, after 2010 also to rural areas

United States: Primary treatment may include ocean outfalls and some biological treatment. Tertiary treatment includes 2-3% of non-discharge treatment, e.g. lagoons, evaporation ponds. Exclude rural areas served by Onsite Disposal Systems

England and Wales: Data refer to the financial year (April to March) until 2000. Independent treatment in 2012 is estimated by assuming that there are 2 persons per property. Data for 2014 refers to England only.

Costa Rica: Data are estimates. Data by type of treatment are not available: the volumes of wastewater are estimated using a coefficient of return of 70%, on the basis of which other data are inferred. In addition, it is common to use the sewage to evacuate storm water, which would cause measurement bias. For more information see http://www.inec.go.cr/