Coliform Bacteria in Well Water: Complete Testing & Treatment Guide

What Are Coliform Bacteria?

Coliform bacteria are a large group of microorganisms found throughout the environment—in soil, on plants, and in the intestines of warm-blooded animals (including humans). Most coliform bacteria are harmless, but their presence in well water serves as an important indicator of contamination.

Think of coliform as a warning sign rather than the danger itself. If coliform bacteria can enter your well, so can more dangerous pathogens like viruses, parasites, and disease-causing bacteria.

Why We Test for Coliform

Testing directly for every possible pathogen would be expensive and impractical. Coliform bacteria are used as "indicator organisms" because:

• They're easy and inexpensive to detect
• They survive in water similarly to many pathogens
• Their presence indicates possible contamination pathways
• Absence of coliform generally means water is safe

Types of Coliform Bacteria

Standard well water tests check for two categories:

1. Total Coliform

This broad category includes all coliform bacteria, many of which exist naturally in soil and aren't directly harmful. A positive total coliform test means:

• Bacteria are entering your well somehow
• A contamination pathway exists
• More serious contamination could follow
• Investigation and treatment are needed

Total coliform alone doesn't confirm fecal contamination, but it indicates vulnerability.

2. E. coli (Escherichia coli)

E. coli is a specific type of coliform found only in the intestines of humans and animals. A positive E. coli test means:

• Fecal matter has contaminated your water
• Human or animal waste is reaching your well
• Dangerous pathogens are likely present
• Immediate action is required

E. coli-positive water should NOT be consumed until treated and retested.

Fecal Coliform

Some labs test for "fecal coliform"—a group that includes E. coli and related bacteria that thrive at body temperature. This is more specific than total coliform but less precise than E. coli testing.

Health Risks of Coliform Contamination

Total Coliform (No E. coli)

Most total coliform bacteria aren't directly harmful. However, their presence indicates your well is vulnerable. The real risk is what else might be entering along with the coliform:

• Viruses (hepatitis A, norovirus)
• Parasites (Giardia, Cryptosporidium)
• Pathogenic bacteria (Salmonella, Campylobacter)

E. coli Contamination

E. coli in well water poses direct health risks:

• Gastrointestinal illness: Nausea, vomiting, diarrhea, stomach cramps
• Urinary tract infections
• Respiratory illness (in some cases)
• Severe complications in vulnerable populations

Who's Most at Risk?

• Infants and young children
• Elderly individuals
• Pregnant women
• People with compromised immune systems
• Those with chronic illnesses

If anyone in your household is at higher risk, take extra precautions with any positive test result.

How Coliform Bacteria Enter Wells

Understanding contamination sources helps you fix the problem permanently:

Well Construction Issues

• Cracked or corroded casing: Allows surface water infiltration
• Damaged well cap: Permits insects, animals, debris entry
• Failed grout seal: Lets surface water flow down alongside casing
• Improper original construction: Shortcuts that create vulnerability
• Old, deteriorated wells: Aging materials fail over time

Surface Contamination

• Flooding: Overwhelms well with contaminated surface water
• Poor drainage: Water pools around wellhead
• Nearby animal pens: Manure runoff reaches well
• Fertilizer application: Close to wellhead

Septic System Problems

• Too close to well: Minimum 100 feet recommended in most areas
• Failing drain field: Sewage enters groundwater
• Overloaded system: Can't process waste properly
• Old or damaged tank: Leaks contaminate soil

Groundwater Issues

• Shallow aquifer: More vulnerable to surface contamination
• Fractured bedrock: Fast pathways for contamination
• High water table: Surface bacteria reach water quickly

Testing Your Well for Coliform

When to Test

• Annually: Minimum recommended frequency
• After flooding: Surface water likely entered well
• After well work: Opening the well introduces contamination risk
• After nearby construction: Can disturb soil and contamination pathways
• If water changes: Different taste, odor, or appearance
• If illness occurs: Unexplained gastrointestinal symptoms
• Before buying property: Required in many states

Where to Get Tested

• County health department: Often offers free or low-cost testing
• State-certified labs: Required for real estate transactions
• Private laboratories: Fast results, may offer pickup
• DIY test kits: Good for screening, not definitive

How to Collect a Sample

Proper sampling technique matters—contamination during collection causes false positives:

1. Use sterile container: Labs provide these; don't reuse bottles
2. Choose the right faucet: Use one without aerator, filter, or hose attachment
3. Disinfect the faucet: Wipe with bleach or flame briefly
4. Run water 2-3 minutes: Clear standing water from pipes
5. Fill carefully: Don't touch inside of cap or container
6. Keep cold: Transport in cooler with ice
7. Deliver quickly: Within 6 hours, or 24 hours maximum

Testing Costs

Interpreting Test Results

Results Format

Results are typically reported as:

• Absent/Present: Simply positive or negative
• CFU/100mL: Colony Forming Units per 100 milliliters
• MPN/100mL: Most Probable Number per 100 milliliters

What the Results Mean

False Positives

Sometimes tests show positive results due to:

• Contamination during sample collection
• Bacteria growing in plumbing fixtures
• Too long between collection and testing

If you get a positive result, retest before taking expensive action. Two positive results confirm the problem.

Shock Chlorination: Step-by-Step

Shock chlorination (also called "shocking" the well) kills existing bacteria by circulating a strong chlorine solution through your entire water system. This is the standard first treatment for coliform contamination.

Before You Start

• Calculate chlorine needed: Based on well depth and casing diameter
• Buy supplies: Unscented household bleach (5.25-8.25% sodium hypochlorite), hose, funnel
• Plan for no water: You'll be without water for 24-48 hours
• Arrange alternative water: Bottled water for drinking, cooking
• Bypass water treatment: Remove or bypass filters, softeners

Chlorine Amount Calculator

Use approximately 3 pints of household bleach per 100 gallons of water in the well.

Don't know your well depth? Check your well record or measure with weighted string.

Step-by-Step Procedure

Step 1: Turn Off Water Heater

Turn off power to the water heater (electric) or set to pilot (gas). Chlorinated water can damage the tank lining.

Step 2: Mix and Add Chlorine

1. Mix bleach with 5-10 gallons of water in a clean bucket
2. Remove well cap (note how it comes off for reassembly)
3. Pour chlorine solution into well
4. Use a clean hose to wash down inside of casing

Step 3: Recirculate

1. Connect a garden hose from an outdoor faucet
2. Run the hose back into the well opening
3. Turn on and recirculate for 15-30 minutes
4. This mixes chlorine throughout the well and washes down the casing

Step 4: Chlorinate Household Plumbing

1. Open each cold water faucet until you smell chlorine, then close
2. Do the same for hot water faucets
3. Flush toilets
4. Run water to washing machine, dishwasher, any other fixtures
5. Include outdoor faucets and irrigation

Step 5: Wait

• Let chlorinated water sit for 12-24 hours (24 hours preferred)
• Don't use any water during this time
• The chlorine needs contact time to kill bacteria

Step 6: Flush the System

1. Connect hose to outdoor faucet
2. Run to area AWAY from septic system and landscaping (chlorine kills bacteria in both)
3. Run until chlorine smell is gone (may take 1-4 hours)
4. Then flush indoor plumbing by running all faucets

Step 7: Retest

• Wait 1-2 weeks after flushing
• Collect sample and submit to lab
• Don't drink water until negative result confirmed

If Bacteria Returns

If coliform comes back after shock chlorination:

• The contamination source wasn't eliminated
• Well may have structural problems
• Ongoing disinfection may be needed
• Professional inspection is recommended

Long-Term Treatment Options

If bacteria keeps returning after shock chlorination, you need ongoing treatment:

UV Disinfection

Ultraviolet light kills bacteria and viruses without chemicals.

• How it works: Water passes through chamber with UV lamp; light damages organism DNA
• Pros: No chemicals, no taste/odor change, effective against many pathogens
• Cons: Requires clear water (sediment blocks UV), needs power, lamp replacement yearly
• Cost: $500-$2,000 installed, $50-$150/year maintenance

Continuous Chlorination

Automatic systems inject small amounts of chlorine into water supply.

• How it works: Chemical feed pump adds measured chlorine dose
• Pros: Proven technology, provides residual protection
• Cons: Requires chemical handling, may affect taste, needs contact tank
• Cost: $800-$2,500 installed, $200-$400/year chemicals

Ozone Disinfection

Ozone gas effectively kills microorganisms.

• How it works: Ozone generator injects O3 into water
• Pros: Very effective, no residual chemicals, improves taste
• Cons: Higher cost, more complex, no residual protection
• Cost: $1,500-$4,000 installed

Fix the Source (Best Option)

Rather than ongoing treatment, eliminating contamination is better:

• Replace well cap: $50-$200
• Repair casing: $500-$3,000
• Install well liner: $2,000-$6,000
• Repair septic system: Varies widely
• Improve surface drainage: $500-$2,000
• Drill new well: $5,000-$15,000+ (last resort)

Prevention Tips

Well Maintenance

• Inspect well cap annually—should be tight, with intact gasket
• Ensure proper grading slopes away from wellhead
• Keep area around well clear of debris, chemicals, animal waste
• Maintain 100+ foot separation from septic systems
• Never pile snow near wellhead (contaminated runoff in spring)

Regular Testing

• Test annually even without symptoms
• Test after any flooding or well work
• Keep records of all test results

Septic System Care

• Pump septic tank every 3-5 years
• Don't overload with excess water
• Never put harmful chemicals down drains
• Address slow drains or sewage odors immediately

After Flooding

• Assume well is contaminated
• Don't use water until tested
• Shock chlorinate before retesting
• Have well professionally inspected if submerged

Cost Summary

Frequently Asked Questions