Coliform Bacteria in Well Water: How It Gets In

A positive test for coliform bacteria in well water means something from the surface found a way into your well. Most coliform won't make you sick on its own, so treat it like a warning light. Drink bottled or boiled water until a retest comes back clean. Then find the opening, or the bacteria will keep coming back.

What does a positive coliform test actually mean?

It means the lab found bacteria that live in soil, plants and animal waste, and most of them are harmless. But if coliform can get in, worse things can follow the same path.

So check the next line on the report for E. coli, which comes from human or animal waste. If it's there, stop drinking the water today, even for brushing teeth. Mississippi State's extension guide says to use bottled or boiled water, then retest for E. coli (Mississippi State University Extension).

How does coliform bacteria get into a well?

At Austin Drilling, we find coliform bacteria in well water almost always comes in from the top. A sealed well draws water from below the soil where these bacteria live. So we start at the wellhead and work down, checking these spots first:

1. A loose, cracked or missing well cap, or a torn vent screen.
2. Casing that ends at ground level, where rain can pool around it.
3. A cracked casing or a failed seal between the casing and the soil.
4. A septic tank or drain field sitting too close to the well.
5. Recent pump or plumbing work that wasn't disinfected afterward.

In South Carolina, a private well has to sit at least 75 feet from a septic tank or tile field (SC Regulation 61-71). The state raised that from 50 feet, so older homes can sit closer than today's rule allows.

Is coliform common after a storm or flood?

Flooding is a common cause of a sudden positive test. If floodwater covered your wellhead, assume the well is contaminated until it's disinfected and tested. State guidance says to use bottled or boiled water until then (SC DES, Private Wells: What to Do Before and After Storms). If your well was not flooded, the same sheet says its water is likely unchanged.

What should you do after a positive test?

Get safe water for drinking and cooking first, then have the well inspected before anyone pours bleach down it. Shock chlorination kills what's in the well right now, and our page on shock chlorination for well water explains how that works. But if the cap is cracked, the bacteria ride back in with the next rain.

Once the opening is fixed and the well is disinfected, retest. State guidance recommends testing 7 to 10 days after disinfection. Kits come from a local health department or DES regional office, and the sample goes back the same day you collect it. Austin Drilling can also pull a sterile sample during a site visit, which our free well water testing page covers.

A second positive means the first gap wasn't the only one. That's when we look harder at the casing, and our page on well casing repair walks through those options. Wells near pasture may also need water treatment as a backstop, just never as the whole plan.

How often should a well be tested for bacteria?

Test at least once a year. The EPA says to test private wells every year for total coliform bacteria, nitrates, total dissolved solids and pH (EPA, Protect Your Home's Water). Test right away after a flood, a well repair, or any change in taste, smell or color.

Who can find where the bacteria is getting in?

A licensed well company can track it down. Austin Drilling has been tracking down coliform bacteria in well water across the Midlands and Upstate for 66 years. Call us in West Columbia at (803) 926-5402 or Newberry at (803) 926-7080, Monday through Friday, 7am to 6pm. We'll find how it got in and close it up for good.

FAQ

Is coliform bacteria in well water dangerous?

Total coliform alone usually isn't what makes people sick, but it shows a path exists for things that can. E. coli on the report means stop drinking the water.

Does coliform go away on its own?

It can test clean for a while and then return, because the next heavy rain carries more in through the same opening.

Can I drink the water while I wait for results?

State guidance says to use bottled or boiled water until your results show the water is safe.

Can a well test positive after pump work?

Yes, which is why the EPA says to test after any well repair. Ask whether the well was disinfected afterward.