Assessing the Risks of Potable Water Reuse in Context

The committee that wrote the National Research Council report conducted an analysis that compares the estimated risks of drinking water from two potable reuse projects to a de facto reuse scenario in which five percent of the source water comes from wastewater discharged upstream after secondary treatment. The assumed de facto reuse conditions of scenario 1 are likely typical in many places and are generally perceived as safe. In scenario 2, treated wastewater is allowed to filter slowly through surface soils into an aquifer (also called soil aquifer treatment) before potable reuse. In scenario 3, advanced treatment techniques including microfiltration, reverse osmosis, and advanced oxidation are employed before the water is injected into an aquifer and used as a source of drinking water. Click here to see an illustration of the three scenarios.

The analysis compared the risks of exposure to four pathogens (adenovirus, norovirus, Salmonella, and Cryptosporidium) and 24 chemical contaminants including pharmaceuticals, personal care products, natural hormones, industrial chemicals, and byproducts from water disinfection processes. The graph below shows only the four pathogens; click here for the full set of data on the other 24 chemical contaminants.

Relative risk, shown on a logarithmic scale, posed by selected pathogens in a typical de facto reuse scenario (1), compared to two potable reuse scenarios (2, 3). The smaller the number, the lower the relative risk. For example in Scenario 2, the risk of illness due to Salmonella is estimated to be less than 1/100th of the risk due to Salmonella in Scenario 1. Overall, the results indicate the risk of exposure to these pathogens from drinking reclaimed water does not appear to be any higher than the risk experienced in at least some current drinking water treatment systems.

Click here to see the data on which this table is based.

The results suggest that the risk of exposure to certain microbial and chemical contaminants from drinking reclaimed water does not appear to be any higher than the risk experienced in at least some current drinking water treatment systems—and may, in fact, be orders of magnitude lower.

The analysis revealed that carefully planned potable water reuse projects should be able to provide a level of protection from -waterborne illness and chemical contaminants comparable to—and, in some cases, better than—the level of protection the public experiences in many drinking water supplies across the nation. However, the committee pointed out that the analysis was presented as an example and should not be used to endorse certain treatment schemes or to determine the risk at any particular site without site-specific analysis.