OECD residents connected to a wastewater treatment plant

Connected here means actually connected to a wastewater plant through a public sewage network. Individual private treatment facilities such as septic tanks are not covered here.

Independent treatment:
systems of collection, preliminary treatment, infiltration or discharge of domestic wastewater from dwellings generally between 1 and 50 population equivalents, not connected to an urban wastewater system. Examples of such systems are septic tanks. Excluded are systems with storage tanks from which the wastewater is transported periodically by trukcs to an urban wastewater system.

Total public sewerage:
National population connected to a systems of conduits which collects and conducts urban wastewater. Collecting systems are often operated by public authorities or semi-public associations.

Primary treatment:
treatment of (urban) wastewater by a physical and/or chemical process involving settlement of suspended solids, or other process in which the BOD5 of the incoming wastewater are reduced by at least 20% before discharge and the total suspended solids of the incoming wastewater are reduced by at least 50%

Secondary treatment:
treatment of (urban) wastewater by a process generally involving biological treatment with a secondary settlement or other process, resulting in a BOD removal of at least 70% and a COD removal of at least 75%.

Tertiary treatment:
treatment (additional to secondary treatment) of nitrogen and/or phosphorus and/or any other pollutant affecting the quality or a specific use of water (microbiological pollution, colour etc.). The different possible treatment efficiencies (organic pollution removal of at least 95% for BOD, 85% for COD, nitrogen removal of at least 70%, phosphorus removal of at least 80%, and microbiological removal) cannot be added and are exclusive.

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.

Data is displayed at URL provided. To download, select 'Export', then select desired download format.

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.