Virus contamination from operation and maintenance practices in small drinking water distribution systems

Authors: LAMBERTINI, ELISABETTA - University Of California; Spencer, Susan; KIEKE, BURNEY - Marshfield Clinic Research; LOGE, FRANK - University Of California; Borchardt, Mark

Submitted to: Journal of Water and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2011
Publication Date: 12/1/2011
Citation: Lambertini, E., Spencer, S.K., Kieke, B.A., Loge, F.J., Borchardt, M.A. 2011. Virus contamination from operation and maintenance practices in small drinking water distribution systems. Journal of Water and Health. 9:799-812.

Interpretive Summary: Drinking water distribution systems in municipalities in the United States are located underground, and the pipes are often laid in the same trench as the pipes for sanitary sewers. Sanitary sewers are notoriously leaky, releasing wastewater containing human pathogens into the surrounding soil. The close proximity of these two piping systems, clean drinking water and contaminated wastewater, has raised questions as to whether the activities necessary for day-to-day management of distribution systems could result in contamination. Cutting a pipe open or having a water main break accidently creates an obvious opening for contaminants to enter. A less obvious entry point, believed to happen but its importance not understood, is when an event in a distribution system, like closing a valve, creates a wave of negative pressure similar to water hammer in a house. When this happens, the leaks in the distribution system briefly suck water inward instead of pushing water outward, thus bringing surrounding soil into the pipes. This study related contamination levels of human gastrointestinal viruses in the tap water of 14 Wisconsin communities to operation and maintenance procedures the communities conducted in their distribution systems. Installing new pipes, which required opening up the systems, was found to be the activity that posed the greatest risk for virus contamination. Standard maintenance practices such as cleaning water towers and exercising valves to make sure they turn could create negative pressure waves and these activities were shown to have a weak effect in increasing virus levels. Cleaning pipes by hydrant flushing was shown to be beneficial in reducing virus contamination. Knowing when their distribution system could be vulnerable to contamination will help drinking water utilities take preventative measures. More broadly, these findings are relevant to any industry that uses piping for distributing raw or finished product, for example irrigation water or fluid milk, that needs to avoid product contamination from materials outside the piping system.

Technical Abstract: We tested the association of common events in drinking water distribution systems with contamination of household tap water with human enteric viruses. Viruses were enumerated by qPCR in the tap water of 14 municipal systems that use non-disinfected groundwater. Ultra-violet disinfection was installed at all active wellheads to reduce virus contributions from groundwater to the distribution systems. As no residual disinfectant was added to the water, any increase in virus levels measured downstream at household taps would be indicative of distribution system intrusions. Utility operators reported events through written questionnaires. Virus outcome measures were related to distribution system events using binomial and gamma regression. Virus concentrations were elevated in the wells, reduced or eliminated by UV disinfection, and elevated again in distribution systems, showing that viruses were, indeed, directly entering the systems. Pipe installation was significantly associated with higher virus levels, whereas hydrant flushing was significantly associated with lower virus levels. Weak positive associations were observed for water tower maintenance, valve exercising, and cutting open a water main. Coliform bacteria detections from routine monitoring were not associated with viruses. Understanding when distribution systems are most vulnerable to virus contamination, and taking precautionary measures, will ensure delivery of safe drinking water.