Bacteria in well water: fix the well first, then consider UV

The problem: what a coliform result is telling you

Labs don't test for every possible germ. They test for coliform bacteria as an indicator. NC DHHS explains that most coliforms won't likely cause illness, but their presence means disease-causing organisms could also be in the water.^[source] Your report can show three levels:

• Total coliform: a broad group found in soil and on plants, generally harmless in itself. A positive result means surface material is reaching your water.^[source]
• Fecal coliform: a subgroup from the intestines of people and animals. A positive result means sewage or animal waste is getting into the well.^[source]
• E. coli: a subgroup of fecal coliform. NC DHHS describes a positive as a sign of fecal contamination and a high risk of illness from disease-causing organisms.^[source]

Likely causes

Soil normally filters bacteria out of rainwater before it reaches groundwater. NC DHHS notes that poorly built, cracked or unsealed wells give bacteria a path around that filter.^[source] Common culprits include:

• A loose, cracked or missing well cap, or a cap without a screened vent.
• Damaged casing, or ground that slopes toward the wellhead so runoff pools around it.
• Recent work on the well. Well components can let bacteria in when they're opened, which is why NC DHHS recommends testing after repairs or replacements.^[source]
• Flooding. NC DHHS recommends testing after any flood that may have covered the wellhead.^[source]
• A septic system or animal area too close to the well, or other surface sources upslope.

Bacteria do show up in wells around here. A 2023 UNC study of Union County wells listed coliform bacteria and E. coli among the contaminants it observed.^[source] We haven't found a reliable regional percentage, so we won't quote one.

How testing works

North Carolina's required test for new wells includes bacteria. Labs test for total coliform first, and if it's present, they check for fecal coliform or E. coli.^[source] After that, NC DHHS recommends testing every year for total and fecal coliform, and again whenever taste, color or odor changes.^[source]

• Use a sterile bottle from a certified lab and follow its sampling and delivery-time instructions closely. Bacteria samples are time-sensitive.
• Sample from a cold tap without an aerator or filter, after disinfecting the tap opening if the lab instructs.
• After disinfection, retest. The state's well-disinfection guide suggests retesting for bacteria about seven to ten days after chlorinating.^[source]

Our well water testing service can schedule a certified-lab bacteria test along with the rest of your panel, and our new-well test results guide shows where bacteria appear on the state report.

Treatment, in the right order

1. Step 1

   Inspect and repair the well

   Check the cap, vent, casing, grout and grading. If bacteria are getting in through a defect, no amount of treatment equipment downstream fixes the cause. A certified well contractor handles well repairs.

2. Step 2

   Shock chlorinate

   Shock chlorination puts a strong chlorine solution through the well and plumbing and is typically recommended when tests show bacteria.^[source] The state guide calls for at least a 200 ppm chlorine residual for shock chlorination, letting the solution sit at least 24 hours, then flushing until the chlorine odor is gone, away from your septic system.^[source]

3. Step 3

   Retest

   Retest about seven to ten days later. If bacteria remain, the state guide says the well may need an inspection, including removing any foreign matter, before disinfecting again.^[source]

4. Step 4

   Add a barrier if it keeps coming back

   If the well is sound but bacteria keep returning, or you want ongoing protection, a certified UV system adds continuous disinfection at the point where water enters the house.

Where UV fits, and what it can't do

Ultraviolet treatment passes water past a UV lamp to inactivate microorganisms, with no chemicals added. The standard to look for is NSF/ANSI 55, and specifically a Class A listing, which NSF lists as a disinfection-performance claim. Check the exact model in NSF's listings.^[source] See our UV disinfection page for system types.

• UV is a supplemental barrier. It doesn't seal a cracked casing or keep surface water out. Fix the well first.
• UV doesn't remove anything. It does nothing for arsenic, nitrate, iron, radon or lead, so those still need their own treatment based on a lab test.
• Water has to be clear. Iron, manganese, hardness or sediment can shade or coat the lamp sleeve, so UV usually sits after iron and manganese filtration and a sediment filter.
• No lamp, no protection. UV works only while the lamp is on and within its rated life. Choose a unit with a sensor or alarm, and keep up lamp and sleeve changes.
• Keep testing. Annual bacteria tests still apply with UV in place.

A UV system connects to your main water line and needs electrical power nearby. Here's how installation works.

Lamps and sleeves need regular replacement. A Care Plan schedules them along with your annual bacteria retest.