Well Water Bacteria Test: Coliform & E. Coli Testing
📋 In This Guide
Quick Answer: Test annually and after any contamination event. Get sample bottle from certified lab, collect properly, return within 24 hours. Tests check total coliform and E. coli. Positive results: don't drink, shock chlorinate, retest. Cost: $20-$50.
What You're Testing For
Total Coliform
- Group of bacteria found in environment
- Includes soil bacteria, plant debris
- Most are not harmful themselves
- Indicate possible contamination pathway
- Standard: 0 CFU/100mL (should be absent)
E. Coli
- Type of fecal coliform
- Only comes from intestinal tracts
- Indicates fecal contamination
- Potential for illness
- Must be absent from drinking water
Why Both Matter
| Result | Meaning | Action |
|---|---|---|
| Total coliform: Absent, E. coli: Absent | Water is safe | None needed |
| Total coliform: Present, E. coli: Absent | Possible pathway, not fecal | Shock chlorinate, retest |
| E. coli: Present | Fecal contamination | Don't drink, treat immediately |
When to Test
Annual Testing
- At minimum, test once per year
- Same time each year (spring recommended)
- Creates baseline for your well
Additional Testing After
- Flooding near the well
- Any work on the well
- Septic system problems
- Change in water taste/smell/appearance
- Unexplained illness in household
- New baby or immune-compromised person
- Buying property with a well
More Frequent If
- History of positive tests
- Shallow well (under 50 feet)
- Well in flood-prone area
- Near agriculture or septic
How to Test
Lab Testing (Recommended)
Step 1: Get Sample Container
- Contact certified lab
- Request bacteria sample bottle
- Bottle is sterile—don't open until sampling
- May contain preservative
Step 2: Collect Sample
- Choose outside faucet without aerator/filter
- Remove any attachments
- Clean faucet with bleach or flame (briefly)
- Run water 3-5 minutes (flush standing water)
- Reduce flow, fill bottle
- Don't touch inside of bottle or cap
- Fill to line indicated
- Cap immediately
Step 3: Return Quickly
- Keep cold (cooler with ice)
- Return within 24-48 hours (24 preferred)
- Don't freeze
Home Test Kits
- Available at hardware stores
- Less accurate than lab
- Good for preliminary check
- If positive, confirm with lab test
- Cost: $15-$30
Lab Test Cost
- Bacteria only: $20-$50
- Include nitrate: $40-$75
- Comprehensive panel: $100-$300
Understanding Results
How Results Are Reported
- Absent/Present: Detected or not
- CFU/100mL: Colony forming units (count)
- MPN/100mL: Most probable number
What "Absent" Means
- None detected in sample
- This is the goal
- Safe to drink
What "Present" Means
- Bacteria detected
- Water may not be safe
- Further action needed
False Positives
- Can occur with improper sampling
- Contaminated bottle
- Touched inside of cap
- If positive, may want to resample
If You Test Positive
Immediate Actions
- Stop drinking the water
- Use bottled water or boil water (1 minute)
- Don't use for cooking without boiling
- Can use for flushing, washing (not brushing teeth)
Shock Chlorination
- Disinfects well and plumbing
- Kills bacteria present
- Often resolves single positive
- See our shock chlorination guide
Retest
- Wait 7-14 days after shocking
- Take new sample
- Should come back absent
If Still Positive
- Ongoing contamination source
- May need well inspection
- Check well cap/seal
- Check distance from septic
- May need ongoing treatment (UV, chlorination)
Treatment Options
- UV disinfection: Kills bacteria continuously
- Chlorine injection: Ongoing chlorination
- Fix contamination source: Seal well, repair casing
We use Hach and LaMotte professional water testing equipment for field analysis, with comprehensive lab testing through certified California laboratories.
Frequently Asked Questions
How do I test my well water for bacteria?
Get sterile bottle from certified lab, collect sample properly, return within 24 hours. Lab tests for coliform and E. coli. Cost: $20-$50.
What does it mean if my well tests positive for coliform?
Possible contamination pathway. Shock chlorinate and retest. E. coli positive is more serious—indicates fecal contamination.
How often should I test my well?
Annually at minimum. More often if history of problems, shallow well, or near contamination sources.
Can I drink the water while waiting for results?
If no reason to suspect contamination, yes. If testing after a concern (illness, flooding), boil or use bottled until results.
Do home test kits work?
Give preliminary indication but less accurate. Positive home test should be confirmed by lab. Lab testing is preferred.
Need Water Testing?
See our water testing services for bacteria and other contaminants.
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