- October 14, 2026
- By Fid Thompson
In the first statewide study of well water on Maryland’s farms, University of Maryland water quality specialists found harmful bacteria along with a wealth of information about the factors that affect well contamination.
The study, published last month in PLOS Water, tested 79 wells around the state and found 10% were contaminated with E. coli, while 43% were contaminated with total coliforms, bacteria that indicate the presence of fecal matter in the water and raise health concerns.
“Unlike municipal water, private wells in the United States are not required to be tested. So this study fills a critical gap for Marylanders,” said Rachel Rosenberg Goldstein, associate professor in the School of Public Health (SPH) Department of Global, Environmental, and Occupational Health.
The study analyzed contamination levels against several factors: geographic location, precipitation, and well characteristics such as depth, well cover material and maintenance intervals.
The percentage of wells contaminated with E. coli was higher than in previous studies, said Rosenberg Goldstein, possibly because of the larger sample size or the fact that all samples came from farms, which have multiple possible sources of contamination.
Significant increases in the odds of E. coli presence in wells were found in the far western part of the state such as Allegheny and Washington counties, compared to wells on the Eastern Shore, such as Worcester and Wicomico counties. The disparity could be due to the different geologic makeup of each area, said Rosenberg Goldstein, who has also studied urban water and sewage infrastructure and contamination as a principal investigator of the Grand Challenges Grants Program-funded Water Emergency Team. The team also tested Potomac River water after a historic sewage spill in January.
Precipitation had a somewhat surprising effect: where rainfall was higher in the two weeks before testing, E. coli was less likely to be present. Precipitation usually increases contamination risks, but this new finding could point to the more complex interaction of dry and wet periods preceding rain, when bacteria can be washed away in consistent wet periods.
Wells with concrete covers were significantly more at risk of E. coli presence than those made of plastic or metal. And deeper wells were less likely to have E. coli than shallow wells, defined by the researchers as less than 9 meters deep.
Rosenberg Goldstein worked with SPH doctoral student Cameron Smith and colleagues at UMD Extension, including the recently retired Andy Lazur, University of Maryland Extension Specialist in Water Quality, and biostatistician Raul Cruz-Cano, a UMD alumnus who is now an associate professor at Indiana University Bloomington School of Public Health.
Though the sample size is limited, participant demographics were similar to Maryland farmers overall, when compared to the 2022 Census of Agriculture from the U.S. Department of Agriculture, said Rosenberg Goldstein, suggesting that the results could apply more widely.
“The results highlight the need for private well testing in Maryland and beyond,” said Smith, a graduate assistant in SPH’s Water Quality, Outreach and Wellness (WOW) laboratory. “If we understand the factors that affect contamination, we can better prevent health risks among private well owners.”