Your well water test came back positive for coliform bacteriaColiform BacteriaA group of bacteria used as indicators of potential contamination. Total coliform presence suggests a pathway for pathogens to enter your well.EPA MCL: 0 (no coliform should be present)Learn more → (organisms that signal contamination). This means something has created a path for bacteria to enter your well.
Don't panic — but do act. The type of bacteria determines how urgent the situation is.
Quick Answer
Total coliform positive, E. coli negative: Shock chlorinate your well ($15). Retest in 2 weeks. If bacteria return, install a UV disinfectionUV DisinfectionA chemical-free method that uses ultraviolet light to destroy bacteria, viruses, and other microorganisms by damaging their DNA. Does not change water taste or chemistry.Learn more → (ultraviolet light) system ($400–$800). E. coliE. coliA specific type of coliform bacteria that indicates fecal contamination. Its presence in well water is a serious health concern requiring immediate action.EPA MCL: 0 (any detection requires action)Learn more → (fecal bacteria) positive: Stop drinking the water immediately. Shock chlorinate. Find and fix the contamination source. Install UV for permanent protection.
What Are Coliform and E. coli in Well Water?
Coliform bacteria are a large family of organisms. Most are harmless. But their presence means your well has a weakness. Think of coliform as an alarm — it tells you the door is open[2].
E. coliE. coliA specific type of coliform bacteria that indicates fecal contamination. Its presence in well water is a serious health concern requiring immediate action.EPA MCL: 0 (any detection requires action)Learn more → (a specific type of fecal bacteria) is different. It comes from human or animal waste. Its presence means fecal contamination has reached your water[3]. This is a direct health threat.
Have your water test results? Get a treatment plan based on your exact numbers.
Analyze My Water TestHealth Risks of Bacteria in Well Water
E. coli and other fecal bacteria cause gastrointestinal illness. Symptoms include diarrhea, stomach cramps, nausea, and vomiting[3].
Children, the elderly, pregnant women, and people with weak immune systems face the highest risk. Severe cases can lead to hospitalization.
The EPA sets the MCLMCL (Maximum Contaminant Level)The highest level of a contaminant allowed in public drinking water, set by the EPA. Private wells are not regulated by MCLs, but they serve as the best available safety benchmarks.Learn more → (maximum contaminant level) for both total coliform and E. coli at zero. No amount is acceptable[2].
What Your Bacteria Test Means
| Result | Status | What It Means | What to Do |
|---|---|---|---|
| Absent / Not Detected | Safe | No bacteria found. Well is protected. | Retest annually. |
| Total Coliform: Present | Action Needed | Contamination pathway exists. | Shock chlorinate. Retest in 2 weeks. |
| E. coli: Present | Urgent | Fecal contamination confirmed. | Stop drinking. Shock chlorinate. Fix source. Install UV. |
Common Causes of Bacteria in Wells
- Cracked or damaged well casing: Allows surface water to seep in.
- Faulty or missing well cap: Insects, rodents, and rain enter the well.
- Surface water runoff: Heavy rain washes contaminants into shallow wells.
- Nearby septic system failure: Sewage leaks into groundwater.
- Flooding: Floodwater carries bacteria directly into the well[4].
Finding and fixing the source is critical. Treatment without fixing the entry point is like mopping while the faucet runs.
How to Test for Bacteria in Well Water
Use a certified lab test. Not a DIY strip. The lab will report total coliform and E. coli separately. Cost: $20–$40 for bacteria only[8].
Test at least once per year. Also test after flooding, well repairs, or unexplained stomach illness in your household[1].
3 Ways to Treat Bacteria in Well Water
Step 1: Shock Chlorination (One-Time Reset)
Shock chlorination floods your well with a strong chlorine solution. It kills bacteria throughout the well, pipes, and pressure tank. Cost: about $15 in supplies[9].
Wait 12–24 hours. Flush all taps until the chlorine smell is gone. Retest in 2 weeks. If bacteria are gone, shock chlorination solved it.
Step 2: Fix the Contamination Source
Inspect your well cap, casing, and grout seal. Hire a well contractor if you see cracks or damage. Check the distance from your septic system — it should be at least 50 feet away[5].
This step is critical. Without it, bacteria will return.
Step 3: UV Disinfection (Permanent Protection)
If bacteria return after shock chlorination, install a UV disinfectionUV DisinfectionA chemical-free method that uses ultraviolet light to destroy bacteria, viruses, and other microorganisms by damaging their DNA. Does not change water taste or chemistry.Learn more → (ultraviolet light) system. UV light destroys bacteria, viruses, and parasites by damaging their DNA[7].
It adds nothing to your water. No chemicals. No taste change. The lamp needs replacement once per year ($50–$80).
Cost: $400–$800 for the system. Installation adds $200–$400.
Important: UV requires clear water to work. If your water has ironIronA naturally occurring mineral found in groundwater. Iron causes orange/rust staining on fixtures and laundry and gives water a metallic taste.EPA Secondary MCL: 0.3 mg/L (ppm)Learn more → (dissolved mineral), hardnessHardness (Calcium Carbonate)The concentration of dissolved calcium and magnesium in water. Hard water causes scale buildup in pipes, water heaters, and fixtures.No EPA standard. Soft: <1 gpg. Moderate: 1-7 gpg. Hard: 7-10.5 gpg. Very Hard: >10.5 gpg.Learn more → (calcium and magnesium), or turbidityTurbidityA measure of water cloudiness caused by suspended particles. High turbidity can harbor bacteria and indicates possible contamination pathways.EPA standard for public systems: 1 NTU (max), 0.3 NTU (95th percentile)Learn more → (cloudiness), install pre-filters first.
DIY vs. Professional Installation
Shock chlorination is a DIY job. You need bleach, a hose, and a few hours. Many state extension services publish step-by-step guides[9].
UV systems need plumbing and electrical connections. If you have basic plumbing skills, plan for 3–4 hours. Professional installation adds $200–$400 and includes testing.
What to Do Next
E. coli positive? Stop drinking the water now. Use bottled water until you shock chlorinate and retest clean.
Total coliform only? Shock chlorinate your well. Retest in 2 weeks. If clean, retest again in 3 months to confirm.
Bacteria keep coming back? Install a UV system and hire a well contractor to inspect your casing and cap. Enter your test results in our Water Test Interpreter for a full treatment plan.
Frequently Asked Questions
Is it safe to drink well water with coliform bacteria?
No. Any coliform detection means a contamination pathway exists[2]. Total coliform alone may not cause illness. But it signals that harmful organisms could enter your well. E. coli requires immediate action.
What causes bacteria in well water?
Common causes: cracked well casing, faulty well cap, surface runoff, nearby septic failure, or flooding[4]. Bacteria enter through any gap in your well structure.
How do you get rid of bacteria in well water?
Start with shock chlorination ($15 in supplies). If bacteria return after retesting, install a UV system ($400–$800). Also fix the contamination source — cap, casing, or grout.
How much does a UV water purifier cost?
The system costs $400–$800. Installation adds $200–$400. The UV lamp needs yearly replacement ($50–$80). Total 10-year cost: $1,000–$1,800.
How often should I test my well for bacteria?
At least once per year[1]. Also test after flooding, well repair, or stomach illness. If you had a positive test, retest every 6 months until 2 consecutive clean results.
References
- U.S. EPA. "Ground Water and Drinking Water: Bacteria and Viruses." 2024. https://www.epa.gov/ground-water-and-drinking-water
- U.S. EPA. "National Primary Drinking Water Regulations: Total Coliform Rule." 40 CFR Part 141, 2024. https://www.epa.gov/sdwa
- CDC. "Private Ground Water Wells." Centers for Disease Control and Prevention, 2024. https://www.cdc.gov/healthywater/drinking/private
- Penn State Extension. "Coliform Bacteria in Private Water Systems." College of Agricultural Sciences, 2023.
- Virginia Cooperative Extension. "Bacteria in Household Water." Publication 356-486, 2022.
- Water Quality Association. "Microbiological Contaminants in Water." Technical Resources, 2024. https://wqa.org
- NSF International. "NSF/ANSI 55: UV Disinfection Systems." 2024. https://www.nsf.org
- Minnesota Department of Health. "Coliform Bacteria in Well Water." Well Management Program, 2023.
- NC DHHS. "Shock Chlorination of Wells." Division of Public Health, 2023.
- U.S. EPA. "Revised Total Coliform Rule." Factsheet, 2013. https://www.epa.gov/dwreginfo/revised-total-coliform-rule