A quantitative microbial risk assessment of water reuse for California’s agricultural irrigation

The current drought in California highlights how precious a resource water is to the lives of California residents, the state’s natural ecosystems, and its agricultural economy. Over the last few decades, recycled water — the reuse of treated wastewater — has played an important role in meeting ever increasing demands for water.  Since the early days of water reuse, questions concerning the safety to public health have been raised numerous times.  And, the practice of quantitative microbial risk assessment has responded by evaluating the efficacy of treatment processes on the removal of infectious agents in wastewater, and by assessing quantitatively using risk models, the potential for water reuse to result in infection and disease in human populations through various exposure scenarios.

I was involved in the quantitative microbial risk assessment (QMRA) modeling for a recent review of water reuse for California’s agricultural irrigation.  The QMRA was part of a process that involved input from a panel of experts, who addressed a number of issues relevant to developing assumptions for the QMRA, as well as relevant to the interpretation of the QMRA’s findings.  The panel and QMRA were commissioned by the California Department of Public Health, which recognized the need to reassess risks given the potential for increasing water reuse in agricultural irrigation, improved knowledge of the concentrations of microbial pathogens found in wastewater, and new treatment processes.  The report of the findings from this process is available here.


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