March 10, 2017
Study finds new evidence that viruses and bacteria may be found in some public water supply wells
One year into a two-year study requested by the state Legislature, scientists with the Minnesota Department of Health (MDH) report finding evidence of genetic material, like DNA, from viruses and bacteria in water from some of the state’s public water supply wells. Researchers said more information is needed to determine how and when microbes enter the wells and whether there may be a health risk for people drinking the water.
“We continue to analyze the results of the study to get a better sense of the potential risk,” said MDH Assistant Commissioner Paul Allwood. “Our goal is to better understand the relationship between site-specific factors and the presence of microbial indicators in the wells.”
MDH scientists tested the source water using a method that can tell how much of a microbe’s DNA or RNA is in the water, but does not indicate how long the microbe may have been in the water or if the microbe is capable of causing illness. Finding such evidence of microbes in a drinking water system does not necessarily mean that those consuming water from these systems would become ill, but it does indicate the system may be vulnerable to contamination.
While it’s not yet known how the microbial indicators got into the wells, the study detected indicators in some systems on more than one occasion, and chemical analysis indicated there was a potential pathway for contamination. Health officials will now work with systems to determine how to reduce potential contamination.
The wells involved in the study are from public water systems around the state, serving smaller cities, mobile home parks, apartment buildings, offices, factories, churches, schools and child care facilities.
The 2014 Minnesota Legislature directed MDH to conduct a groundwater virus monitoring project using funding from the state’s Clean Water Fund. The project has two components: a monitoring study divided into two phases and a community illness study. In the first phase of the monitoring study, MDH looked at how often microbes were detected in groundwater by sampling source water from the wells of 82 systems. The systems were randomly selected in order to represent the different geographic and geologic regions of the state. The second phase of the monitoring study, scheduled to be completed by this summer, includes wells with different characteristics than the wells in the first phase. The community illness study, also scheduled to be done by this summer, is designed to see if there is an association between viruses in a community’s water supply and illness in the community.
In the first phase of the monitoring study, scientists collected 478 samples from the 82 systems between May 2014 and April 2015. Researchers found that while the overall presence of microbial indicators in samples was low, a high percentage of wells had at least one detection. Overall, 8 percent of samples tested positive for human viruses and 11 percent tested positive for Salmonella. However, 37 percent of systems had evidence of human viruses and 89 percent of systems had evidence of microbes (including some that don’t cause human illness) detected at least once during the study period.
The intermittent nature of the detections is a reminder that water contamination can come and go very quickly, health officials said. Contamination sources also can change with time. Factors that can affect results include weather conditions such as heavy rain or snow melt, wastewater or manure close to the well, how the well is constructed, aquifer type and well pumping patterns. Further analyses will examine these issues.
“We don’t know exactly how viruses and bacteria might be getting into wells,” said Anita Anderson, project coordinator with MDH. “That’s part of the work we still have to do: looking at the wells, potential sources of contamination and other factors, and figuring out how the contamination is occurring and what can be done about it.”
While a final report is not expected for several months, researchers are notifying system owners with vulnerable wells so they can assess their wells, look for solutions and inform their customers. MDH recently sent letters to the 82 systems, reporting their results and providing options for next steps.
MDH will conduct detailed site investigations for systems with stronger evidence of contamination to see if a contaminant source or a pathway for contamination can be identified. Until the full study is complete, MDH has no specific recommendations to issue. However, any time consumers have concerns about potential water contamination, they have a number of options including: using bottled water, boiling their water for food preparation and drinking or installing a reverse osmosis water filter.
In the next several months, MDH and project partners will complete an analysis of all study results including the community illness study. After completion of the study, MDH will work with systems to determine what recommendations might be warranted to ensure public health. Possible recommendations include:
- Improving prevention measures to keep microbes from getting into wells or aquifers;
- Repairing or replacing problem wells; or
- Adding disinfection to the water treatment process.
“Monitoring for microbes of public health importance is complex and expensive,” Allwood said. “Understanding how they get into aquifers and wells may help us find a cost-effective way to predict problems and take preventive action.”
MDH recommends that both public and private water systems continue to maintain their wells and conduct routine testing of their water supply, and to follow recommended procedures for operating and maintaining septic systems or other contaminant sources. More information is available on the MDH Groundwater Virus Monitoring Study web page.