The call comes from the lab, or the letter arrives in the mail, and the result says: positive for total coliform. Your well water has bacteria.
The first reaction is usually panic. Bacteria in the water. That sounds serious. That sounds like Flint, like a boil water notice, like something that could make your family sick.
Sometimes it is serious. Often it isn't, at least not in the way you're picturing. Understanding what the result actually means is the difference between a sensible response and an expensive overreaction. Or worse, brushing off a real problem.
What Are the Three Types of Coliform Bacteria in Well Water?
Total coliform is a broad category of bacteria that includes hundreds of species found in soil, vegetation, and the digestive tracts of warm-blooded animals. Most total coliform bacteria are not harmful to humans. Their presence in well water matters for a different reason. It tells you a pathway exists for contamination, meaning surface water or soil is somehow reaching your well.
Fecal coliform is a subset of total coliform found specifically in the intestines and feces of warm-blooded animals. A positive fecal coliform result means recent fecal contamination, whether from wildlife, livestock, a failing septic system, or surface runoff from agricultural land. This is a more serious finding than total coliform alone.
E. coli is a specific type of fecal coliform. Most E. coli strains are harmless, but certain strains, particularly E. coli O157:H7, can cause severe illness, as the CDC warns. A positive E. coli result in well water is a serious finding that requires immediate action. Stop drinking the water until the source is identified and the well is treated.
What Causes Coliform in Connecticut Wells
Connecticut's geology and land use patterns create several common pathways for coliform contamination.
Septic system proximity: Connecticut has a high density of private wells and septic systems sitting close together. The state requires a minimum separation distance between a well and a septic system, but older properties may not meet current standards. Even compliant systems can fail or become saturated during heavy rain.
Surface water intrusion: Wells with damaged or improperly sealed casings can let surface water in directly. This is particularly common after heavy rain. The same storms that cause flooding also push surface water into vulnerable wells.
Agricultural runoff: In farming areas, including the Connecticut River Valley and the agricultural towns of Tolland and Windham counties, runoff from fields with animal waste can reach well water. Shallow wells are the most exposed. The Connecticut River Valley has a well-documented nitrate problem from farming that often travels alongside bacterial contamination.
What Should You Do After a Positive Coliform Result?
First: determine which type of coliform was found. Total coliform alone is a different situation from fecal coliform or E. coli.
Second: shock chlorinate the well. This is the standard first response to a positive coliform result. You introduce a high concentration of chlorine into the well to kill bacteria, then flush the system. Your water testing lab or a licensed well contractor can walk you through the process.
Third: retest after shock chlorination. If the result is still positive, the contamination source needs to be identified and addressed.
Fourth: consider a UV disinfection system. For wells with recurring coliform issues, a UV disinfection system installed at the point of entry, certified to NSF/ANSI Standard 55, provides continuous protection against bacteria and viruses without adding chemicals to the water.
A positive coliform result is not a reason to panic. It is a reason to act. And if your well has bacteria issues, it may have other problems too, because the standard mortgage water test doesn't cover most of them.
Want ZIP-level context before deciding whether to test? Enter your ZIP code at CheckYourTap.com to see available public-system or regional monitoring records associated with the ZIP. This is not a test of a tap, well, or property. Free, in 30 seconds.
Keep Reading
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- The Rotten Egg Smell in Your Well Water Is Telling You Something. Listen to It.
Sources: CT DPH Private Well Testing Guidelines; EPA Coliform Bacteria in Drinking Water; NSF International Well Water Testing Guide; CT DPH Well Contractor Licensing Program.
