Total Coliform Bacteria in Well Water

Total coliform is not a single type of bacteria. It refers to a large family of bacteria found naturally in soil, plants, and surface water. Some members of this family also live in the intestines of humans and animals.

Most total coliform bacteria do not cause illness. That might seem strange for something labs test for. The reason is simple: coliform bacteria are easy to detect, and their presence tells you something important about your water system.

Think of total coliform as a canary in the coal mine. If these bacteria can get into your well, other things can too, including disease-causing organisms that are harder to test for.

The CDC describes total coliform as an indicator of sanitary integrity. A positive result suggests there may be a route for contamination to enter your water supply. (CDC)

Private wells are different from public water systems. No government agency monitors your well or requires you to test it. You are responsible for making sure your water is safe. (EPA)

Total coliform testing is the most practical first check for any private well because:

• It is inexpensive compared to comprehensive water panels
• Results come back quickly, often within a few days
• It catches problems you cannot see, smell, or taste

Contamination in well water often has no warning signs. Your water can look perfectly clear and still carry bacteria. Testing is the only way to know.

These terms get mixed up often. Here is the simple breakdown:

• Total coliform is the broad group. It includes many types of bacteria found in the environment.
• Fecal coliform is a smaller subset. These bacteria are more closely linked to waste from humans and animals.
• E. coli is a specific type within that group. Its presence strongly indicates fecal contamination.

When labs find total coliform in your sample, they typically run an additional check for E. coli on the same sample. (WA DOH)

Why this matters for you: A total coliform positive without E. coli is concerning but manageable. An E. coli positive is more urgent and requires faster action.

Total coliform can enter your well water in several ways. Understanding the source helps you fix the problem permanently.

Wellhead Problems

The most common cause. Bacteria can enter through:

• A damaged or loose well cap
• Missing vent screens that let insects in
• Cracks in the casing or seal
• Well casing sitting too low, allowing surface water to pool around it

Surface Water and Flooding

Heavy rain, flooding, or snowmelt can overwhelm protective barriers. Wells in low-lying areas are more vulnerable. Many health departments recommend testing after any significant flood event.

Septic Systems

A failing septic system, or one located too close to your well, can contribute bacteria over time. Even properly functioning systems may pose a risk if soil conditions allow contamination to travel.

Sampling Errors

Sometimes the water is fine, but bacteria got into the sample during collection. Touching the inside of the bottle, sampling from a dirty faucet, or delays in getting the sample to the lab can all cause false positives. (CDC)

The CDC recommends testing private well water for coliform bacteria at least once per year. (CDC)

Beyond annual testing, consider testing your well:

• After any flooding or major storm event
• After repairs to your well or pump
• If you notice changes in taste, odor, or water appearance
• When buying a home with a private well
• If anyone in your household becomes ill with gastrointestinal symptoms
• If infants, elderly family members, or immunocompromised individuals live in your home

Building a testing history helps you spot patterns. A well that tests positive after every heavy rain tells you something different than a single unexpected positive.

Bacteria testing requires careful sample collection. Unlike some water tests, bacteria samples are time-sensitive and easy to contaminate.

Choose a Certified Lab

The CDC recommends using a state-certified laboratory for well water testing. Your local health department can provide a list of approved labs in your area. (CDC)

Collect the Sample Correctly

Most labs provide sterile bottles with specific instructions. Follow them exactly. General best practices include:

• Use only the sterile bottle provided by the lab
• Do not rinse the bottle or touch the inside of the cap
• Remove and clean the faucet aerator if instructed
• Run the water for a few minutes before collecting
• Fill the bottle without letting it overflow

Get the Sample to the Lab Quickly

Bacteria samples typically need to reach the lab within 24 to 30 hours. Keep the sample cold during transport. Check with your lab about their specific requirements.

Cost and Turnaround

A basic coliform bacteria test typically costs between $20 and $50 at most state labs. Results usually come back within 2 to 5 days. Prices vary by location and lab.

Most lab reports show total coliform results as simply "Present" or "Absent" (sometimes "Detected" or "Not Detected"). Some labs report a number using methods like MPN (Most Probable Number) or CFU (Colony Forming Units).

For private wells, the key question is binary: was coliform detected or not?

Understanding the Reference Standard

For public water systems, the EPA sets a Maximum Contaminant Level Goal (MCLG) of zero for total coliform and E. coli. (EPA)

Private wells are not regulated by these rules, but zero remains the goal. Any detection warrants follow-up.

What Your Results Mean

• Total coliform absent, E. coli absent: Your water passed this test. Continue with annual testing.
• Total coliform present, E. coli absent: Your well may have a vulnerability. Retest promptly and inspect your wellhead.
• E. coli present: This indicates possible fecal contamination. Stop using the water for drinking until you resolve the issue and confirm with retesting.

A positive total coliform result requires action, but not panic. Follow these steps in order:

Step 1: Check for E. coli

Look at your report carefully. If E. coli is also detected, treat this as urgent. Use bottled water or another safe source for drinking and cooking until you resolve the problem.

Step 2: Retest Your Well

Sampling errors cause many false positives. Collect a new sample using careful technique and send it to the lab. The CDC recommends retesting after any unexpected positive result. (CDC)

Step 3: Inspect Your Wellhead

Walk out to your well and look for obvious problems:

• Is the cap secure and undamaged?
• Are vent screens in place?
• Is water pooling around the casing?
• Are there visible cracks or gaps in the seal?
• Signs of insects, rodents, or nesting?

Fix any obvious defects, then retest.

Step 4: Consider Shock Chlorination

If retesting still shows coliform, many well owners and health departments recommend disinfecting the well with chlorine (shock chlorination). This is especially common after repairs or contamination events.

After disinfection, wait the recommended time and retest to confirm the problem is resolved.

Step 5: Get Professional Help If Needed

Persistent positives after disinfection and repairs may indicate a deeper problem with well construction. A licensed well contractor can evaluate casing integrity, seals, and potential contamination sources. Your local health department can also help interpret results. (CDC)

You cannot sterilize the environment around your well, but you can maintain the barriers that keep bacteria out.

Protect Your Wellhead

• Keep the cap intact, tight, and properly screened
• Make sure the ground slopes away from the well so water drains away, not toward it
• Keep the area around your well clear of debris, chemicals, and animal waste
• Inspect the wellhead at least twice a year

Test After Any Work or Events

Any time your well is opened for pump work, repairs, or maintenance, there is a risk of introducing bacteria. Test after these events, even if everything looks fine.

Keep Records

Save your lab reports. Note dates of any repairs, flooding, or changes. If you ever need to troubleshoot recurring problems, this history will help you and any professionals you work with.

Testing your well water is the first step toward knowing it is safe. Use a state-certified laboratory for accurate results you can trust.

Find well water testing providers in your state using our directory, or contact your local health department for recommendations specific to your area.