E. coli and total coliform presence in private drinking water wells on Maryland farms: Determination of the impact of well properties, geographic, and precipitation factors

Over 43 million individuals in the United States use private wells for drinking water, but these wells are not regulated by the Safe Drinking Water Act. Unmaintained private wells on farms could become contaminated from pathogens from various potential sources including on-farm animal waste. Microbial contaminants in private wells could increase infectious disease risks among well users, therefore it is important to conduct well water testing and keep a well maintained system. We distributed surveys and collected water samples from private wells that supply drinking water on farms from all seven regions of Maryland. Our objective was to evaluate the presence of total coliforms and E. coli in private wells and the impact of well, geographic, and precipitation factors on the bacterial contamination risk. Eighty-four water samples were collected from 79 private wells on farms across Maryland. Samples were analyzed for total coliforms and E. coli with U.S. EPA Method 1604. Data were analyzed using Fisher’s Exact test and logistic regression. Forty-three percent (34/79) of the sampled wells were positive for total coliforms and 10% (8/79) were positive for E. coli . Total coliform presence was significantly associated with county ( p = 0.02), region ( p < 0.01), and well condition description ( p = 0.02). E. coli presence was significantly associated with region ( p < 0.01), geological province type ( p < 0.01), county ( p = 0.04), and wellhead cover type ( p = 0.03). Based on the multivariable logistic regression, wells that were described as being in okay or fair condition had significantly lower odds of total coliforms compared to wells described as being in good or excellent condition ( p = 0.03), suggesting a lack of understanding about actual well conditions. There was a significant decrease in the odds of E. coli presence as precipitation levels 14 days prior to sampling increased ( p = 0.02) . These results emphasize the importance of private well water testing, particularly for farmers.