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Issue Profile

Water Resources

Water Resources tracks how well countries treat wastewater from households and industrial sources before releasing it back into the environment.

What it measures: The proportion of collected wastewater that is treated.

Why we include it: The sole indicator in this category is Wastewater Treatment. Untreated sewage can disrupt the functioning of downstream ecosystems. Wastewater is comprised of domestic grey-water (water from baths, sinks, washing machines, and kitchen appliances) and black-water (water from toilets), as well industrial wastewater that may have additional chemical contaminants. It typically contains nutrients and chemicals that pollute natural water systems, resulting in a range of impacts from algal blooms to biological endocrine disruption. In rural areas, where pit latrines or septic systems are prominent, pollutants tend to be dispersed in the environment. In urban areas, however, functioning sewage systems that collect and treat wastewater concentrate the pollutants into discrete discharges that are more easily treatable. The practice of water treatment is vital for the health of aquatic systems, provides health benefits for local residents, and ensures that clean water is available for re-use. Good wastewater management is especially relevant for areas facing more significant impacts of climate change and rapid population growth, since such areas may face more constrained water resources in the future.

Where the data comes from: This novel dataset was developed by the Yale Center for Environmental Law & Policy (YCELP). (See Creating the Wastewater Treatment Indicator.) It represents a combination of environmental statistics reported from national ministries along with official statistics from the Organization for Economic Cooperation and Development (OECD), the United Nations Statistical Division (UNSD), and the Food and Agriculture Organization of the United Nations (FAO), with inputs from the Pinsent Masons Water Yearbook and additional expert advice.

What the target is: 100% for Wastewater Treatment. For more information, click here

Description: Management of water resources is important for both human and ecosystem health. However, despite the centrality of water to sustain all human life and ecosystem vitality, there are many challenges that prevent measuring water quality at the global scale (See The Challenge of Measuring Global Water Quality). Because of the lack of comparable data across countries, the importance of landscape-level factors in determining water quality, among other challenges, we are currently unable to include a direct output measure assessing how countries perform in terms of maintaining water quality. 

As a second-best indicator, we turn towards drivers of water quality, specifically the treatment of wastewater as an important component of overall management. Up to 90 percent of the discharged wastewater produced in developing countries is untreated when it is released back to the environment. Untreated wastewater contributes to high pollution levels, eutrophication of water bodies, high coliform bacteria counts, and, in extreme cases, hypoxia and fish-kills, as described below. The Wastewater Treatment indicator measures how countries engage in treatment efforts at the municipal level, weighting the results for multiple municipalities by city population size as measured by the coverage of the sewerage network. It is distinct from other, related indicators such as the JMP’s “Access to Sanitation” metrics which only survey latrine access at a basic level and do not speak to water quality or ecosystem health.

Wastewater is the water that has been used by households and industries that, unless treated, no longer serves a useful purpose. Gray-water is from household sinks, washing machines, and kitchen appliances and contains nutrients and chemicals. Black-water comes from toilets. Left untreated, nutrients and chemicals go into natural water systems where they cause harm to the environment and human health. Wastewater treatment requires a system for collection—normally through sewage pipes—and treatment at different levels, which are described below. Treatment plants can be public or private utilities that serve a given municipality. (See Primary vs. Secondary: Types of Wastewater Treatment),

Even where wastewater treatment plants exist, they may not have the capacity to treat all of the water collected. This situation can arise when the population of a city outpaces the development of new treatment facilities or because of a lack of funding. As a result, many wastewater treatment facilities discharge excess wastewater directly into waterways or coastal areas, and, in other cases, the existing treatment plants are simply dysfunctional.

Ideally, the Wastewater Treatment indicator would measure the proportion of all household waste that is treated. Unfortunately, this is impossible as figures on total wastewater generation are unavailable for most countries. Furthermore, while centralized treatment systems may be appropriate for dense urban areas, in many rural areas, decentralized treatment systems may be the better solution. But because rural areas do not always provide data, this indicator is limited to an urban scope. This presents an obvious problem for rapidly growing places where many new residents live in areas outside the municipality’s core infrastructure, and hence are not connected to centralized sewage treatment facilities. 

Thus, this indicator assesses the proportion of wastewater that is treated for those households that are connected to the sewerage system. It measures wastewater that mostly comes from household sources, but in some cases industrial sources contribute if they share the municipal collection network. This varies on a country-by-country basis. Despite the known limitations, expert review confirms that this measure still provides a useful metric against which to judge country performance.

Wastewater pollution can lead to algal blooms from eutrophication, which is the addition of enough nutrients to an ecosystem to cause certain plant species such as algae to proliferate at the expense of other species. Eutrophication, in turn, can lead to fish die-offs because algae depletes the water of oxygen. This can lead to economic hardship for those people living off such aquatic resources. Shellfish poisoning may also occur since such organisms tend to accumulate biological and chemical contaminants and consumers often eat shellfish raw.1 Similarly, biological effects such as endocrine-disruption can occur due to the presence of pharmaceutical products or chemicals in waterways.

Harmful human health effects can also result from untreated wastewater. There are a host of bacterial, viral, and protozoan organisms that can survive in human waste and fecal matter, most notably the bacterium Escherichia coli (or E. coli), which can cause various forms of diarrhea. Other pathogens include the bacteria Vibrio choleraeShigella spp., and Campylobacter spp., as well as noroviruses and rotaviruses. As a consequence, diseases such as bancroftian filariasis worm-caused schistosomiasis can result from human consumption of untreated wastewater.2 Fortunately, many of these problems can be ameliorated by good wastewater treatment, since treating has been shown to reduce pathogen concentrations by orders of magnitude.

Treatment is done in sequential steps that have different levels of complexity depending on the resources available. (See The Waste-Reuse Energy Nexus,) The typical range of treatment options is primary, secondary, and tertiary treatment. Primary treatment involves basic processes such as settlement tanks to remove suspended solids from water and to reduce the biochemical oxygen demand (BOD). Secondary treatment involves biological degradation that allows bacteria to decompose elements in the wastewater more, further reducing nutrient levels and BOD. The highest form of wastewater treatment is tertiary treatment, which is any process that goes beyond the previous steps and can include the use of sophisticated technology to further remove contaminants or specific pollutants. Tertiary treatment is typically employed to remove phosphorous or nitrogen content, which cause eutrophication

While the Wastewater Treatment indicator would ideally consider more advanced levels of treatment, data availability and gaps restrict consideration to only the wastewater that receives “at least primary treatment” because it’s the only common definition available for globally comparable measurement.

Water and sanitation policy discussions in the past decade have gone beyond basic access measures, with increasing focus on wastewater treatment. This change shows that interest is shifting toward including water quality as well as water quantity in performance metrics.3 (See The Future of Water Resource Measurement). However, there is global need for more and better data on wastewater generation, treatment, and use.

Discussions on the post-2015 international development agenda and SDGs at the UN will potentially lead to a specific goal on water, which may include specific targets on wastewater treatment.4 The SDGs, which must be “aspirational, universal, communicable, and measurable,” aim to create global targets for all countries between 2015 and 2030. They are based on the model of the MDGs set in 2000. Following the 2013 World Water Week, YCELP hosted an expert workshop in Stockholm, Sweden. Experts at the meeting provided strong encouragement for the development of this indicator.

The development of an SDG on wastewater treatment is critical since it will encourage higher levels of performance and likely result in better data for future monitoring. This effort represents a first important step in this direction. (See Evolution of Water Quality Indicators in the EPI).


1 Shuval, H. (2003) Estimating the global burden of thalassogenic diseases: human infectious diseases caused by wastewater pollution and the marine environment. Journal of Water and Health 1:53-64.

2 Baum, R., Luh, J., and J. Bartram. (2013) Sanitation: A global estimate of sewerage connections without treatment and the resulting impact on MDG progress. Environmental Science & Technology 47:1994-2000.

3 Bjornsen, P. (2013) Post-2015 targets and their monitoring: SDG on water. Presentation at World Water Week. 1-6 September 2013. Stockholm, Sweden.

4 Ibid.


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