SDG 6.3.1. Wastewater Treatment

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

As part of Target 6.3 (“improve water quality by reducing pollution, … halving the proportion of untreated wastewater …”), Indicator 6.3.1 is meant to assess what proportion of wastewater is being safely treated. The UN aims to assess three types of wastewater flows: domestic (household sewage), industrial, and total (which would include other point sources such as service facilities in addition to domestic and industrial wastewater). However, limited data are available for most countries on industrial and total wastewater treatment, so we focus here on domestic wastewater.

The domestic wastewater indicator is closely related to the sanitation indicator (6.2.1). Conceptually, Indicator 6.2.1 is meant to protect the health of the sanitation user, while Indicator 6.3.1 is meant to protect the environment, although - as I point out in Chapter 16 - sanitation and wastewater treatment are best thought of as a continuous chain of services meant to protect both human health and the environment.

global wastewater flow pathways — Safe and unsafe pathways for domestic wastewater at the global scale. Source: UN report.

As noted in Chapter 16, there are multiple pathways by which human waste can enter the environment, and the goal of monitoring Indicator 6.3.1 is to quantify these pathways in each country. The image to the left (similar to the Shit Flow Diagram for Lima shown in Figure 16-4) summarizes the results at the global scale:

Networked sanitation (sewers): Globally, most sewered wastewater is delivered to a wastewater treatment plant (WWTP), although 10% is discharged directly into the environment without reaching a WWTP (because of limitations in the collection system) and 14% of the wastewater that does reach a WWTP is discharged without adequate treatment (because of treatment plant limitations).
Septic tanks: This category is meant to also include other on-site well-contained sanitation options, such as pit latrines. Globally, 65% of waste in these systems is either never emptied or buried on site, which are considered safe disposal options. Another 29% is emptied and delivered to a WWTP, although not all of this waste is treated effectively. The most problematic category - tanks and latrines that are emptied and disposed of locally - is estimated to account for 6% of waste in these systems.
Other sanitation: This corresponds to open defecation and other uncontained sanitation options, which are always considered unsafe.

map of global wastewater treatment — Domestic wastewater treatment (Indicator 6.3.1) by country. Red: 0-50%; Yellow: 50-75%; Green: 75-100%. Source: UN Water.

Not surprisingly, the fraction of domestic wastewater that is safely treated varies dramatically around the world (see map), although the low level of treatment reported in some moderate- and high-income countries (such as Brazil, China, Russia, and Italy) is disappointing.

progress over time in wastewater treatment — Change in domestic wastewater treatment (Indicator 6.3.1) over time. Source: UN Water.

Data for this indicator are relatively recent, so it is hard to monitor progress over time. However, the limited data shown in this figure suggest that the regions that struggle the most with wastewater treatment - Sub-Saharan Africa and Northern Africa & Western Asia - are not making progress and may even be regressing.

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