Coliform bacteria or E. coli in your well
Coliform bacteria are a warning sign that surface water or something else is getting into your well. E. coli means fecal contamination. Don't drink the water until it's fixed and retested.
Don't drink untreated water, use it for cooking, or use it to brush your teeth. Use bottled water, or bring water to a rolling boil for 1 minute. If anyone in the home is sick, call your doctor.
What your result means
| Result | What it means | Drink the water? |
|---|---|---|
| Total coliform: absent | No sign of bacterial contamination | Yes |
| Total coliform: present, E. coli absent | Something is letting bacteria in. Usually not an immediate danger, but needs fixing | Boil it or use bottled water until fixed |
| E. coli: present | Contamination from human or animal waste | No. Use bottled water, or boil at a rolling boil for 1 minute |
What to do next
- Inspect the well. Look for a loose or cracked cap, a damaged casing, or water pooling around the wellhead. A sanitary, sealed well cap is inexpensive and fixes many cases.
- Check what's nearby. Septic systems, livestock, and low ground where water collects can all be sources.
- Shock-chlorinate the well. This disinfects the well and the plumbing. Penn State Extension publishes step-by-step instructions.
- Retest 1 to 2 weeks later, after the chlorine has been fully flushed out.
- If bacteria come back, fix the source, and consider continuous treatment such as an ultraviolet (UV) light system.
How common it is in Pennsylvania
Very common. In more than 22,000 Penn State well tests, 44% were positive for coliform bacteria and about 1 in 10 for E. coli. See how your county compares.
How often to test
Penn State recommends testing for coliform bacteria every year, and after flooding, well repairs, or any change in taste, color, or smell.
When to call a professional
Call a licensed well driller if your casing or cap is damaged, or if bacteria keep coming back after shock chlorination. Call a water treatment professional if you need UV treatment.
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