Indicator 6.3.1 Proportion of domestic and industrial wastewater flows safely treated

Indicator 6.3.1: Proportion of domestic and industrial wastewater flows safely treated

Target 6.3: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally

United Nations Human Settlements Programme (UN-Habitat)

World Health Organization (WHO)

United Nations Statistics Division (UNSD)

Definitions:

This indicator measures the volumes of wastewater which are generated through different activities, and the volumes of wastewater which are safely treated before discharge into the environment. Both of these indicators are measured in units of 1000 m³/day, although some data sources may use other units that require conversion. The ratio of the volume treated to the volume generated is taken as the ‘proportion of wastewater flow safely treated’.

Wastewater flows will be classified into industrial, services, and domestic flows, with reference to the International Standard Industrial Classification of All Economic Activities Revision 4 (ISIC). To the extent possible, the proportion of each of these waste streams that is safely treated before discharge to the environment will be calculated.

Concepts:

Total wastewater generation and treatment can be quantified at the national level, and wastewater can also be disaggregated into different types of flows, based on ISIC categories. Domestic wastewater generated by private households, as well as wastewater generated by economic activities covered by ISIC categories, may or may not be pre-treated on premises before discharge to either the sewer for further treatment or directly to the environment, as shown in Figure 1.

Figure 1: Schematic Representation of wastewater sources, collecting systems and treatment

(modified from wastewater loading diagram, OECD/Eurostat 2018).

The main sources of wastewater include wastewater from households, services and industries, i.e. point sources of one or more pollutant(s) that can be geographically located and represented as a point on a map. Diffused pollution from non-point sources such as runoff from urban and agricultural land can contribute quite significantly to wastewater flows (Figure 1), and therefore its progressive inclusion in the global monitoring framework will be important. Presently, it cannot be monitored at source and its impact on ambient water quality will be monitored under indicator 6.3.2 “Proportion of bodies of water with good ambient water quality”.

Differentiating between the different wastewater streams is important as policy decisions need to be guided by the polluter pays principle. However, wastewater conveyed by combined sewers usually combines both hazardous and non-hazardous substances discharged from different sources, but also runoff and urban stormwater, which cannot be separately tracked and monitored. As a consequence, although the flow of wastewater generated can be disaggregated by sources (domestic, services industrial), the treated wastewater statistics are most commonly disaggregated by type (e.g. urban and industrial) and/or level of treatment (e.g. secondary) rather than by sources.

Total wastewater flows can be classified into three main categories (see ‘disaggregation section’ for details:

• Industrial (ISIC divisions 05-35)
• Services (ISIC divisions 45-96)
• Domestic (private households)

Wastewater treatment can be classified into three main categories (see ‘disaggregation section’ for details:

• Primary
• Secondary
• Tertiary

Where possible, treatment will additionally be classified into either on-premises or off-premises treatment.

Domestic wastewater: Wastewater from residential settlements which originates predominantly from the human metabolism and from household activities.

Industrial (process) wastewater: Water discharged after being used in, or produced by, industrial production processes and which is of no further immediate value to these processes. Where process water recycling systems have been installed, process wastewater is the final discharge from these circuits. To meet quality standards for eventual discharge into public sewers, this process waste-water is understood to be subjected to ex-process in-plant treatment. Cooling water is not considered here. Sanitary wastewater and surface runoff from industries are also excluded here.

Total wastewater generated is the total volume of wastewater generated by economic activities (agriculture, forestry and fishing; mining and quarrying; manufacturing; electricity, gas, steam and air conditioning supply; and other economic activities) and households. Cooling water is excluded.

Urban wastewater: Domestic wastewater or the mixture of domestic wastewater with industrial wastewater and/or runoff rain water.

Wastewater: Wastewater is water which is of no further value to the purpose for which it was used because of its quality, quantity or time of occurrence. Cooling water is not considered here.

Wastewater discharge: The amount of water (in m3) or substance (in kg BOD/d or comparable) added/leached to a water body (Fresh or non-fresh) from a point source.

Wastewater treatment: Process to render wastewater fit to meet applicable environmental standards or other quality norms for recycling or reuse.

A clear specification of the terminology and methodology for wastewater statistics is essential to contribute to harmonising international data collection practices and SDG 6.3.1 reporting. The objective of indicator 6.3.1 is to cover households and the entire economy, and to build on the existing international methodology for global monitoring wastewater generation and treatment. This approach reduces the monitoring burden that SDG reporting can impose on countries, and provides well-defined and internationally comparable variables for global data analysis and use by policymakers and urban/land planners.

Data are extracted from a number of pre-existing sources:

• Indicator tables from the UNSD/UNEP data collection on environment statistics

https://unstats.un.org/unsd/envstats/qindicators (refer to “Inland Water Resources”)

• Country files from the UNSD/UNEP data collection on environment statistics (https://unstats.un.org/unsd/envstats/country_files)
• Website of Eurostat water statistics (https://ec.europa.eu/eurostat/web/environment/water)
• Website of OECD water statistics (https://stats.oecd.org/index.aspx?DataSetCode=water_treat#).
• Country files from the WHO/UNICEF Joint Monitoring Programme for Water Supply, Sanitation and Hygiene (JMP) data collection on safely managed sanitation services, and the reports referenced therein
  (https://washdata.org/)

National Statistical Offices (NSOs) are the primary responsible authorities for providing data to be used for global statistics. NSOs may draw on data collected or compiled by relevant national or other authorities, such as ministries, municipalities, or regulatory authorities.

There is a relative lack of knowledge about the volumes of wastewater generated and treated, because wastewater statistics are in an early stage of development in many countries and not regularly produced or reported. Monitoring is relatively complex, costly, and data are not systematically aggregated to the national level and/or accessible; especially industrial wastewater data which are in general poorly monitored and seldom aggregated at national level.

To some extent, this may be explained by the fact that a large proportion of the industrial water requirements are covered by the use of private systems using non-public/drinking water supply (groundwater, rivers and wells) which are not systematically included in the national statistics.

Diffused pollution from non-point sources such as runoff from urban and agricultural land can contribute significantly to wastewater flows, and therefore its progressive inclusion in the global monitoring framework will be important. Presently, it cannot be monitored at source and its impact on ambient water quality will be monitored indirectly under indicator 6.3.2 on the proportion of bodies of water with good ambient water quality.

Different types of wastewater have different degrees of contamination and pose different levels of threat to the environment and public health. Some data exist on the pollutant loading in terms of BOD5 and COD (kg O2/day), but these are not as widely available as data on volumes and will not be used at present for indicator 6.3.1. It is anticipated that future data drives will include more information on pollutant loadings that could be eventually featured in SDG 6.3.1 reporting.

Finally, whether wastewater is classified as safely treated or not depends on the wastewater treatment plant’s compliance rate to the effluent standards (i.e. performance). Many wastewater plants produce effluent which does not meet quality standards, due to improper design or loading. Effluent standards rely on both national and local requirements, as well as on specific water uses and potential reuse options, so that this approach may not provide strictly comparable variables between countries. For the purposes of global monitoring, in the absence of data on compliance, technology-based proxies will be used, in which compliance is assumed if the treatment plant provides at least secondary treatment.

The amount of wastewater generated is calculated by summing all of the wastewater generated by different economic activities and households. Wastewater flows are expressed in units of 1000 m3/day, although some data sources may use other units that require conversion.

The amount of wastewater safely treated is calculated by summing all of the wastewater flows which receive treatment considered equivalent to secondary treatment or better. This wastewater flow is expressed in units of 1000 m3/day, although some data sources may use other units that require conversion.

The proportion of wastewater flows which are safely treated is calculated as a ratio of the amount of wastewater safely treated to the amount of wastewater generated.

2024-09-27

United Nations Human Settlements Programme (UN-Habitat)

World Health Organization (WHO)

United Nations Statistics Division (UNSD)

The domestic portion of wastewater treated is closely linked to indicator 6.2.1a on the “proportion of population using safely managed sanitation services”, and draws upon some of the same data sources.

The indicator is also directly linked to indicator 6.3.2 on the “proportion of bodies of water with good ambient water quality”, because unsafe wastewater treatment leads to degradation in quality of the receiving waters. It directly informs progress towards target 6.3 and is strongly linked to target 6.6 on water-related ecosystems, as well as target 14.1 on marine pollution (coastal eutrophication).

2