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Case Study

Jan 22, 2014

Creating the Wastewater Treatment Indicator

Despite the critical nature of wastewater treatment for freshwater quality, no global databases exist to measure it. Decision makers are discussing water quality in the context of United Nations Sustainable Development Goals (SDGs) (see: The EPI and the SDGs), highlighting the need for metrics, and the EPI team has worked in parallel with global water experts to conceptualize an indicator to assess wastewater treatment performance—the latest attempt of its kind. This indicator can now provide a valuable baseline by which to measure progress. After all, whether countries treat wastewater effluent says a lot about how those countries manage their overall water quality.

The Yale Center for Environmental Law & Policy team initially researched as widely as possible to track down every existing source of data on wastewater treatment. After conducting an extensive literature review, we found that no single database existed that was comprehensive enough to develop a global indicator. So the team decided to make its own dataset. In what was an innovation for the EPI, the team went country-by-country to find data wherever available, and, after a burst of research activity, eventually found enough data to put this issue on the Index.

However, there were challenges in the process. Wastewater data, we found, were often reported at only local or regional scales, limiting the study to a mainly urban scope. Data were also reported from various sources ranging from national state-of-the-environment reports to the annual reports from private utilities. They were also reported sparsely through time. On top of that, definitions for “wastewater” varied. For instance, many sources did not make it clear whether the effluent they were describing was from industrial, municipal, or household waste. Often it was a combination of a few, which is reflected in the indicator. Many reports also did not clarify whether the level of treatment was primary, secondary, or tertiary, and so the EPI indicator covers them all (see: Primary vs. Secondary Wastewater Treatment). Reported statistics also had to be parsed for whether they referred to populations served or volumes of water treated.

The final dataset combines the team’s country-level findings with official statistics from the Organization for Economic Cooperation and Development, the United Nations Statistical Division, the Food and Agriculture Organization of the United Nations, and inputs from the Pinsent-Masons Water Yearbook. In cases where country-level data were not available, city-level data for major cities was used. In a few other cases, the team had to make judgment calls based on evidence, using peer-reviewed literature and conversations with in-country experts. To address consistency, multi-year averages were used, and, to ensure environmental rigor, the final treatment values were weighted by sewerage connection rates to create the final indicator. 

Despite the early challenges of its construction, this intensive effort was worthwhile in the end. The international community now has a starting point by which to judge this major driver of both ecosystem and public health.