Bacteria in Well Water: Signs, Causes & Treatment Options

Bacterial contamination is one of the most common—and most serious—problems affecting private wells. Unlike municipal water, your well water isn't automatically tested or treated, making regular testing essential. This guide explains the types of bacteria found in wells, health risks, testing requirements, and effective treatment options for San Diego County homeowners.

📋 In This Guide

• Types of Bacteria in Well Water
• Health Risks
• Warning Signs of Bacterial Contamination
• Common Causes of Contamination
• Testing Your Well Water
• Shock Chlorination
• Ongoing Treatment Options
• Prevention Strategies
• Frequently Asked Questions

Types of Bacteria in Well Water

Laboratory testing typically looks for two categories of bacteria:

Total Coliform Bacteria

Coliform bacteria are a broad group that includes bacteria from soil, vegetation, and animal/human waste. Their presence indicates that contamination pathways exist—even if the specific coliform found isn't harmful.

• What it means: Potential contamination pathways exist
• Health risk: Most coliform bacteria aren't harmful themselves
• Action needed: Investigate source, may need shock chlorination

E. coli (Escherichia coli)

E. coli is a specific type of coliform found only in human and animal intestines. Its presence definitively indicates fecal contamination.

• What it means: Fecal contamination is present
• Health risk: Can cause serious gastrointestinal illness
• Action needed: Stop drinking water immediately, treat and retest

Other Bacteria of Concern

• Iron bacteria: Not harmful but causes rusty stains, slime, and odor
• Sulfur bacteria: Creates hydrogen sulfide ("rotten egg" smell)
• Legionella: Can cause Legionnaires' disease (rare in cold water)

Health Risks

The health effects of bacterial contamination depend on the type and amount of bacteria present:

Acute (Short-Term) Effects

• Nausea and vomiting
• Diarrhea (sometimes bloody)
• Stomach cramps and pain
• Fever and chills
• Headache and fatigue

High-Risk Populations

Some people are more vulnerable to waterborne illness:

• Infants and young children: Underdeveloped immune systems
• Elderly: Weakened immune response
• Pregnant women: Risk to both mother and fetus
• Immunocompromised: HIV/AIDS, chemotherapy patients, organ recipients

Warning Signs of Bacterial Contamination

Unfortunately, dangerous bacteria often leave no visible signs. However, watch for:

Critical point: You cannot smell, taste, or see most harmful bacteria. The only reliable way to know if your water is contaminated is laboratory testing.

Common Causes of Bacterial Contamination

Surface Water Intrusion

• Damaged or missing well cap
• Cracks in well casing
• Flooding around wellhead
• Improperly sealed annular space

Septic System Problems

• Septic system too close to well (minimum 100 feet required)
• Failed or overflowing septic system
• Improperly maintained drain field

Animal Activity

• Rodents or insects entering through damaged cap
• Livestock waste runoff
• Dead animal in well casing

Well System Issues

• Contamination during pump service or repair
• Old, deteriorated casing
• Shallow well susceptible to surface contamination

Testing Your Well Water

When to Test

• Annually: Baseline testing every year
• After flooding: Any time water reaches the wellhead
• After pump service: Any work that opens the well
• After illness: Unexplained GI illness in household
• When buying property: Always test before closing
• Change in water: Any change in taste, odor, or appearance

How to Collect a Sample

1. Use sterile containers provided by the laboratory
2. Remove aerators from faucets
3. Clean faucet with bleach solution
4. Run water for 2-3 minutes before collecting
5. Fill container without touching inside
6. Keep refrigerated and deliver within 24 hours

Testing Costs

• Total coliform/E. coli: $25-$50
• Iron bacteria: $30-$60
• Comprehensive panel: $150-$300

Shock Chlorination

Shock chlorination (also called well disinfection) uses high concentrations of chlorine to kill bacteria throughout your well system. It's the first-line treatment for bacterial contamination.

When Shock Chlorination Works

• One-time contamination events (flooding, pump service)
• New well construction
• After casing or wellhead repairs
• Iron bacteria problems (combined with physical cleaning)

The Shock Chlorination Process

1. Calculate chlorine needed: Based on well depth and diameter
2. Mix chlorine solution: Typically household bleach diluted
3. Pour into well: Down the casing
4. Recirculate: Run water through system and back into well
5. Let sit: Minimum 12-24 hours contact time
6. Flush system: Until chlorine odor is gone
7. Retest: Wait 7-14 days, then test again

Shock Chlorination Costs

• DIY: $25-$50 (materials only)
• Professional service: $150-$400

Ongoing Treatment Options

If shock chlorination doesn't solve the problem—or if contamination keeps recurring—you need ongoing treatment.

UV (Ultraviolet) Disinfection

Best for: Most residential applications

• How it works: UV light damages bacteria DNA, preventing reproduction
• Effectiveness: 99.99% kill rate for bacteria, viruses, and protozoa
• Pros: No chemicals, no taste change, low operating cost
• Cons: Requires pre-filtration, needs electricity, annual bulb replacement
• Cost: $500-$1,500 installed, $50-$100/year maintenance

Continuous Chlorination

Best for: Ongoing contamination, iron bacteria

• How it works: Chlorine injection at wellhead with retention time
• Effectiveness: Very effective with proper dosing
• Pros: Proven technology, addresses iron/manganese too
• Cons: Chemical handling, taste issues, requires carbon filter
• Cost: $1,000-$3,000 installed, $200-$400/year chemicals

Ozone Treatment

Best for: Complex water quality issues

• How it works: Ozone gas oxidizes and kills bacteria
• Effectiveness: Excellent, faster than chlorine
• Pros: No residual taste, addresses multiple contaminants
• Cons: Higher cost, more complex system
• Cost: $2,000-$5,000 installed

Prevention Strategies

Well Construction and Maintenance

• Maintain proper sanitary seal at wellhead
• Ensure well cap is intact and pest-proof
• Grade ground away from wellhead for drainage
• Annual visual inspection of wellhead
• Repair casing cracks promptly

Setback Distances

California requires minimum distances between wells and contamination sources:

• Septic tank: 50 feet minimum
• Septic leach field: 100 feet minimum
• Animal enclosures: 100 feet minimum
• Manure storage: 100 feet minimum

Frequently Asked Questions