Well Water Coliform: What It Means & How to Fix It

If you just got a positive test result

Shock your well first, then address the underlying cause

A positive coliform result means bacterial contamination is present. Stop drinking unfiltered well water until the issue is resolved. Shock chlorination eliminates the current contamination. A UV system or continuous chlorination prevents recurrence. The source of contamination — surface water intrusion, a cracked casing, nearby septic — also needs to be identified.

What coliform bacteria actually is

Total coliform is a group of bacteria used as an indicator of water quality. Their presence doesn't necessarily mean sewage contamination — coliform bacteria exist naturally in soil and on vegetation. But their presence in well water indicates a pathway for surface water to enter your well, which could also allow pathogens to enter.

E. coli is a subset of coliform bacteria. A positive E. coli result specifically indicates fecal contamination — a more serious finding that requires immediate action.

Coliform vs E. coli — what's the difference?

Total coliform positive, E. coli negative	Surface contamination likely — less severe, still needs treatment
Both total coliform and E. coli positive	Fecal contamination confirmed — requires immediate action, do not drink untreated water
E. coli positive alone	Rare — treat as fecal contamination

Immediate steps after a positive test

Stop drinking or cooking with unfiltered well water
Use bottled water until the issue is resolved
Shock chlorinate the well — see our guide below
Retest 1–2 weeks after shock chlorination
If test is still positive, identify the source of contamination
Install permanent treatment — UV system or continuous chlorination

How to shock chlorinate your well

Calculate your well's water volume (depth × diameter²)
Use unscented household bleach (5.25–8.25% sodium hypochlorite)
Mix bleach with water and pour into well casing
Run each faucet until you smell chlorine, then shut off
Let chlorinated water sit for 12–24 hours
Flush all faucets until chlorine smell is gone
Wait 1–2 weeks and retest

Shock chlorination is a temporary disinfection — it kills current bacteria but doesn't prevent recontamination. A permanent solution is required.

Permanent treatment options

UV (ultraviolet) disinfection	Best option for most homes. UV light kills 99.99% of bacteria, viruses, and cysts without chemicals. Low maintenance, no ongoing chemical cost. Install on the main line after sediment filtration.
Continuous chlorination	Chlorine dosing pump injects small amounts of bleach into the water line. Effective but requires ongoing chlorine supply and a carbon filter downstream to remove taste/odor.
Reverse osmosis (point of use)	RO at the kitchen tap removes bacteria for drinking water only — doesn't treat whole house. Good addition but not a complete solution.

Finding and fixing the source

Treating the symptom without fixing the source means it will recur. Common contamination sources:

Cracked or deteriorated well casing — allows surface water in
Poorly sealed well cap — insects, rodents, or runoff entering
Nearby septic system — especially after heavy rain
Flooding or surface runoff reaching the well
Old, shallow, or dug wells — inherently more vulnerable than drilled wells

A licensed well contractor can inspect your casing and seal. This is worth doing even after successful treatment — without fixing the source, contamination will return.

Springwell UV Systems →

Well Water Coliform: What to Do After a Positive Test