Confirming the need for virus disinfection in municipal subsurface drinking water supplies

Authors: EMELKO, MONICA - University Of Waterloo; SCHMIDT, PHILIP - University Of Waterloo; Borchardt, Mark

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2019
Publication Date: 3/26/2019
Citation: Emelko, M.B., Schmidt, P.J., Borchardt, M.A. 2019. Confirming the need for virus disinfection in municipal subsurface drinking water supplies. Water Research. 157(15):356-364. https://doi.org/10.1016/j.watres.2019.03.057.
DOI: https://doi.org/10.1016/j.watres.2019.03.057

Interpretive Summary: Contrary to popular perception groundwater supplies for drinking water are not always pure. Under some conditions disease-causing microorganisms from the fecal wastes of people and livestock can contaminate groundwater and pose a health risk. However, public water systems oftentimes do not disinfect groundwater before consumption, and it is not fully understood what level of disinfection is needed to reduce health risk. Our study shows for norovirus, which causes severe gastrointestinal illness and is sometimes found in groundwater, that disinfection would need to remove 99.99% of the virus to reduce illness risk to levels deemed acceptable by US public health officials. We further show our disinfection estimate is highly variable because the relationship between the number of noroviruses ingested and the risk of illness is highly variable. Nonetheless, our findings lay out an approach that is useful for estimating the benefits of groundwater disinfection, not just for noroviruses, but other waterborne pathogens as well, and we identify areas in which more research is needed to improve this approach.

Technical Abstract: Enteric viruses pose the greatest acute human health risks associated with subsurface drinking water supplies, yet quantitative risk assessment tools have rarely been used to develop health-based targets for virus treatment in drinking water sourced from these supplies. Such efforts have previously been hampered by a lack of consensus concerning a suitable viral reference pathogen and dose-response model and difficulties in quantifying pathogenic viruses in water. A reverse quantitative microbial risk assessment (QMRA) framework and quantitative polymerase chain reaction data for norovirus genogroup I in subsurface water supplies were used herein to evaluate treatment needs for subsurface drinking water supplies. Norovirus was not detected in over 90% of samples, which emphasizes the need to consider the spatially and/or temporally intermittent patterns of enteric pathogen contamination in subsurface water supplies. Collectively, this analysis reinforces existing recommendations that a minimum 4-log treatment goal is needed for enteric viruses in groundwater in absence of well-specific monitoring information. This result is sensitive to the virus dose-response model used as there is approximately a 3-log discrepancy among virus dose-response models in the existing literature. This emphasizes the need to address the uncertainties and lack of consensus related to various QMRA modelling approaches and the analytical limitations that preclude more accurate description of virus risks.