Executive Summary 

Sustainable Development Goal (SDG) target 6.3 seeks to halve the proportion of untreated wastewater discharged into water bodies and includes two complementary indicators to monitor progress: the proportion of domestic and industrial wastewater flows safely treated (Indicator 6.3.1) and the proportion of bodies of water with good ambient water quality (Indicator 6.3.2). Indicator 6.3.1 aims to track the percentage of wastewater flows from different point sources (households, services, industries and agriculture) that are treated in compliance with national or local standards (UN-Water, 2017). The disaggregation and analysis of wastewater volumes and pollution loads by different sources can help identify heavy polluters, and consequently, apply the “polluter pays” principle to eliminate dumping, minimize the release of hazardous chemicals and improve treatment (UN-Water, 2018).

This report presents a summary of available data on total wastewater flows generated and treated in 2015, as well as disaggregated analyses on flows from industrial sources in 2015 and households in 2020. The monitoring of the total and industrial components of indicator 6.3.1 relies on the aggregation of standardized national-level statistics previously validated by governments. The corresponding flows of wastewater generated and treated have been extracted from two existing harmonized international frameworks (the United Nations Statistics Division (UNSD)/United Nations Environment Programme (UNEP) Questionnaire on Environment Statistics and the Organisation for Economic Co-Operation and Development (OECD)/Eurostat Joint Questionnaire on Inland Waters) and by contacting additional national institutions and ministries or statistical offices. Data for the year 2015 have been selected based on data availability for analysis of the 2021 update of the total and industrial components of the indicator. In 2015, in the 42 countries (representative of 18 per cent of the global population) reporting both generation and treatment of total wastewater flows, 32 per cent received at least some treatment. The proportion of industrial wastewater flow treated was 30 per cent, and could only be calculated for 14 countries (representing 4 per cent of the global population).

The limited data available on total and industrial wastewater flows therefore indicate that proportions of flows being safely treated are low, even among high-income countries, which were more likely to report data. Consequently, there are insufficient data to produce global and regional estimates. The household component of the indicator has been reported separately from that of the total and industrial components due to its  distinct methodological approach of producing estimates of flows generated and safely treated using a combination of nationally reported data, and in their absence, a set of assumptions. The household wastewater analysis draws on data from the UNSD/UNEP and OECD/Eurostat questionnaires, as well as data compiled directly from national statistical agencies, regulators, line ministries, utilities and the Joint Monitoring Programme for Water Supply, Sanitation, and Hygiene (JMP). Overall estimates (global, regional, and national) of household wastewater flows generated and safely treated have been reported as being for 2020, although data for individual components in the calculation were derived from multiple (but most recently available) years in many cases. Globally, 56 per cent of household wastewater flows were safely treated in 2020 (extrapolated from data from 128 countries representing 80 per cent of the global population).

Wide disparities among the regional proportions of household wastewater safely treated were discovered (ranging from 25 per cent to 80 per cent by SDG region), indicating that progress remains uneven across the globe. Although this report reveals that data completeness remains a challenge, the reporting of this indicator remains important for the stimulation of progress on safe wastewater management and for advocating for improved national monitoring programmes that will address data deficiencies. For countries that lack national strategies and targets for the safe treatment of wastewater, improving the monitoring of indicator 6.3.1 may also attract greater attention towards the sector.

Investments in both centralized and decentralized wastewater conveyance and treatment systems are needed in many countries and regions to minimize direct discharges to the environment while ensuring that collected flows are safely treated prior to discharge or reuse. The monitoring of wastewater flows generated by different sources and economic activities is key to the enforcement of regulation (including discharge permits) in order to reduce pollutant discharges and protect water resources. The monitoring of wastewater flows treated will support the shift towards a circular economy in which wastewater is considered a valuable resource. Quality and up-to-date wastewater statistics contribute to the momentum towards achieving SDG 6, as they can be used to support sustainable water resources management and safe wastewater strategies that are both needed to ensure access to water and sanitation for all by 2030.

Key messages

• SDG indicator 6.3.1 tracks the percentage of wastewater flows that are safely treated before discharge or reuse. Wastewater flows are classified into three main categories: (i) total, (ii) industrial, and (iii) households, each of which have been reported on individually. • Data on total and industrial wastewater generation and treatment rely on the existing standardized methodologies associated with the official statistics extracted from Eurostat, OECD and UNSD databases. Generally, there was a lack of accurate data reporting on wastewater volumes generated and treated, highlighting the challenges of complexity, cost and aggregation at national levels.

• The calculation of country estimates for the household component relies on a combination of official statistics and strategic assumptions to fill data gaps and fully characterize a “household wastewater management chain”. This chain represents the proportion of flows generated, collected and safely treated for sewer and septic tank wastewater streams. While data are more broadly available and reported for the household component versus the total and industrial components, the same aforementioned issues about data quality and completeness apply.

• Total wastewater treated: In the 42 countries reporting standardized national-level data previously validated by governments for both generation and treatment of total wastewater flows, 32 per cent of all wastewater flows generated from point sources in 2015 received at least some treatment (although they were not necessarily safely treated), representing 18 per cent of the global population.

• Industrial wastewater treated: In the 14 countries reporting standardized national-level data previously validated by governments for both generation and treatment of industrial wastewater flows, 30 per cent of all wastewater flows from industrial sources in 2015 received at least some treatment, representing 4 per cent of the global population. • Household wastewater safely treated: Globally, 56 percent of all wastewater flows generated by households in 2020 were collected and safely treated (meaning they were treated by secondary or higher processes or that effluent discharges met relevant standards). This global estimate is based on individual estimates produced for 128 of 234 countries and territories representing 80 per cent of the global population. Approximately 57 percent of PROGRESS ON WASTEWATER TREATMENT - 2021 X all household wastewater flows that were generated in 2020 were delivered into sewers, while 24 per cent flowed into septic tanks, and the remaining 19 per cent were generated by households with all other types of sanitation, including those with no toilets at all. Of the household wastewater flows directed into sewers, approximately three-quarters (78 per cent) were safely treated at the point of discharge (either having been discharged according to standards or treated by at least secondary treatment processes). Of the flows directed into septic tanks, nearly half were collected and safely treated on- or off-site (48 per cent), while flows generated by households with all other types of sanitation (i.e. pit latrines and open defecation) were considered not safely treated.

• Municipal wastewater utilities are an important source of consistent reported data, but there are currently extremely low levels of reporting of industrial wastewater statistics. Data scarcity, particularly for independent treatment systems and industrial discharges, reveals the low priority given to managing pollution from these sources. It is therefore necessary to strengthen regulatory mechanisms (for example, national standards and discharge permits) for all sources of wastewater and to carry out monitoring and enforcement of local service providers and industry to drive improvements to both treatment and monitoring. Data aggregation and national-level reporting by regulators in coordination with statistical offices is needed for the transparent assessment of national and global progress and for informing national strategies and plans.

• The disaggregation of wastewater volumes and pollution loads by sources according to households, services and industries can help identify heavy polluters, and consequently, apply the polluter pays principle to eliminate dumping, minimize the release of hazardous chemicals and better protect human health, aquatic ecosystems and biodiversity. Improving the monitoring and management of wastewater flows by economic sectors should be incorporated in national adaptation strategies and plans to increase society's resilience to climate change and implement equitable and sustainable integrated water resources management.

• For household wastewater in particular, it is urgently necessary to ensure that flows generated are discharged either into sewer lines or on-site storage and treatment systems, such as septic tanks with leach fields. In settings where septic tanks (or other forms of independent treatment) are common, national inspection programmes may support efforts to promote the correct operation, maintenance and functionality needed to not only meet monitoring requirements, but also to protect the surrounding environment and public health. • Improving wastewater management is not only fundamental for protecting drinking water resources from fecal contamination and waterborne diseases (for example, cholera, typhoid fever or hepatitis) and protecting aquatic ecosystems from nutrient input (eutrophication) and chemical and plastic pollution; but also for mitigating and adapting to climate change. Developments in response to the COVID-19 pandemic have also demonstrated the utility of wastewater-based disease surveillance (for example, monitoring SARS-CoV-2 RNA).

• The promotion of the safe reuse of treated wastewater should be prioritized in policies and monitored in accordance with the ambition of SDG target 6.3. Safe reuse may also support the achievement of other goals by making beneficial use of water, nutrients and energy recoverable from wastewater, and adapting to growing urban population needs (SDG 2 and 11), transitioning to a circular economy (SDG 12) and adapting to water scarcity induced by climate change (SDG 13).

• In the future, some water quality parameters routinely monitored in wastewater treatment plant effluents could also be included as part of indicator 6.3.1, to estimate the organic load eliminated by wastewater treatment, and the resulting load discharged into the environment. Such enhancements to the monitoring of the indicator would serve to strengthen the relationship and interconnectedness between indicator 6.3.1 and indicator 6.3.2, which focuses on ambient water quality

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