A lab report that says coliform bacteria were found in your well is unsettling, but it comes with a clear set of next steps from the health agencies. Here is what the result means, what to do in the short term and how the cause is found and fixed.
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What coliform bacteria are
Nebraska’s DWEE describes coliform as a group of bacteria found in the digestive tracts of humans and animals. Some types are beneficial and help with digestion; others, like E. coli, may cause illness. Florida’s Department of Health explains why the test matters: many types of bacteria are generally not harmful, but their presence is an indication that other harmful bacteria, viruses or parasites may be present.
That is why total coliform is on EPA’s and CDC’s list of yearly tests for every private well. It is a signal that something is getting into the water.
What a positive result tells you about the well
DWEE puts it directly: coliform of any kind in a drinking water sample suggests there may be structural issues with the well or a source of contamination nearby. Florida’s Department of Health lists the routes by which bacteria reach a well: poorly maintained septic systems, livestock areas, fertilizer, and poorly built wells.
Short-term steps
- Contact your health department. EPA’s advice when a contaminant exceeds a health standard is to contact your public health department for the steps to follow.
- Boil drinking water in the short term. DWEE says water can be boiled for one minute to kill the bacteria before it is used for drinking and food preparation. If the same test showed high nitrates, do not boil: DWEE warns that boiling concentrates nitrates.
- Re-test to confirm. EPA advises having the well re-tested to confirm the contaminant and its level, at a certified laboratory.
- Have the well inspected. DWEE says a certified well contractor should inspect the well as soon as possible.
Positive bacteria test? Give your ZIP code and say what the lab found.
Finding the cause
Disinfecting a well without fixing how bacteria got in is a short-term fix at best. The inspection looks for the way in. EPA’s checklist for owners is a good guide to what gets looked at:
- Cracked, corroded or damaged casing
- A broken or missing well cap, or a cap that does not seal
- Surface seals that have settled or cracked
- Ground that slopes toward the well instead of away
- A septic system that needs pumping or inspection
- Livestock areas, fertilizer use or other sources nearby
- Recent flooding, or recent work on the well
EPA’s chart of reasons to test lists coliform bacteria for nearby intensive agriculture, alongside nitrate, nitrite and pesticides, so a test for those may be worth adding.
Disinfecting the well
Once the cause is found and fixed, the well itself is disinfected. EPA says high bacteria can sometimes be controlled by adding disinfection to a well, such as chlorine, ozone or ultraviolet light. Disinfecting a well with chlorine is what people mean by well chlorination or shock chlorination of a well. The amount and method depend on the well, so follow your health department’s guidance or have the well pro do it, and keep a record of it, as EPA asks owners to do.
If bacteria keep coming back after the well has been fixed and disinfected, continuous treatment may be discussed, such as a UV system: see UV light for well water and well water treatment. EPA also notes that, depending on the contaminant, its level and the condition of the well, some owners need a new source of water or a new well.
Test again
After disinfection, test again at a certified laboratory to confirm the bacteria are gone, then keep to the yearly schedule. EPA also says to test immediately after any repair to the well, and after flooding near it. The well water testing page has the full schedule.
Send what the lab found and your ZIP code. An independent local well pro can contact you.
Questions people ask
Is coliform in well water dangerous?
Nebraska DWEE says some coliform are beneficial and others, like E. coli, may cause illness. Florida’s Department of Health says the presence of bacteria is an indication that other harmful bacteria, viruses or parasites may be present. Ask your health department about your result.
Can I drink well water with coliform if I boil it?
Nebraska DWEE says water can be boiled for one minute in the short term before drinking or cooking, unless nitrates are also high, in which case boiling is not advised.
What is shock chlorination of a well?
Disinfecting the well with chlorine. EPA lists chlorine among the ways to control high bacteria. Follow your health department’s guidance or have a well pro do it.
What is your well doing?