Private wells serve over 23 million U.S. households, yet unlike municipal water systems, they are not regulated by the EPA or tested by any government agency. The responsibility for water quality falls entirely on the homeowner.
This guide covers the three most critical contaminant categories for well owners — PFAS, nitrates, and bacteria — along with testing schedules, treatment options, and the latest regulatory developments in 2026.
PFAS: The "Forever Chemicals"
What Are PFAS?
Per- and polyfluoroalkyl substances (PFAS) are a group of over 12,000 synthetic chemicals used since the 1940s in nonstick cookware, firefighting foam (AFFF), waterproof clothing, food packaging, and industrial processes. They are called "forever chemicals" because they do not break down naturally in the environment.
How PFAS Enter Well Water
- Military bases: AFFF firefighting foam used in training exercises is the largest known source
- Airports: Fire suppression training areas contaminate surrounding groundwater
- Industrial sites: Manufacturing facilities that used or produced PFAS
- Landfills: PFAS-containing consumer products leach into groundwater
- Wastewater treatment plants: Cannot fully remove PFAS; treated effluent can contaminate aquifers
- Biosolids: PFAS-containing sewage sludge applied to agricultural land
Health Effects
PFAS exposure has been linked to (EPA, 2024):
- Cancer: Kidney cancer, testicular cancer, and bladder cancer
- Immune suppression: Reduced vaccine effectiveness, increased susceptibility to infection
- Thyroid disease: Interference with thyroid hormone production
- Reproductive issues: Decreased fertility, pregnancy-induced hypertension
- Cholesterol: Increased LDL cholesterol levels
- Liver damage: Elevated liver enzymes
- Developmental effects: Low birth weight, accelerated puberty
2026 Regulatory Standards
The EPA finalized the first-ever national drinking water standards for PFAS in April 2024:
- PFOA: 4 parts per trillion (ppt) Maximum Contaminant Level (MCL)
- PFOS: 4 parts per trillion (ppt) MCL
- Combined PFAS: Hazard Index MCL for mixtures of PFHxS, PFNA, HFPO-DA, and other PFAS
While these standards legally apply only to public water systems, they establish the safety benchmarks that private well owners should use.
State-level developments:
- New York launched a private well PFAS testing and mitigation rebate pilot program in 2026 for six counties
- Washington State aligned PFAS compliance values with federal MCLs effective January 15, 2026
- Multiple states now offer free or subsidized PFAS testing for private wells
PFAS Testing
- Cost: $200-$500 for a comprehensive PFAS panel
- Important: Standard home water test kits do NOT detect PFAS — laboratory analysis is required
- Frequency: Test at least once; retest every 2-3 years if near known contamination sources
PFAS Treatment
- Reverse osmosis (RO): Removes 90-99% of PFAS at point-of-use. Cost: $200-$600 for under-sink units
- Granular activated carbon (GAC): Whole-house filtration removes 60-90% of PFAS. Cost: $1,500-$5,000
- Ion exchange resins: Most effective for specific PFAS compounds. Cost: $2,000-$6,000
- Combination systems: GAC + RO provides the most comprehensive protection
For a broader look at filtration options, see our guide to the best water filtration systems for well water.
Nitrates: The Agricultural Threat
What Are Nitrates?
Nitrates (NO3-) are naturally occurring compounds that become dangerous contaminants at elevated levels. The EPA Maximum Contaminant Level is 10 mg/L (milligrams per liter).
How Nitrates Enter Well Water
- Agricultural fertilizer: The primary source in rural areas — nitrogen fertilizers leach into groundwater
- Animal waste: Concentrated animal feeding operations and manure application
- Septic systems: Improperly functioning or poorly sited septic systems
- Natural deposits: Some geological formations naturally contain nitrates
- Stormwater runoff: Carries fertilizers and animal waste into shallow aquifers
Health Effects
- Blue baby syndrome (methemoglobinemia): Nitrates reduce the blood's ability to carry oxygen in infants under 6 months. Can be fatal without treatment
- Cancer risk: The National Cancer Institute (2023) found associations between high nitrate exposure and colorectal, ovarian, thyroid, kidney, and bladder cancers
- Thyroid disruption: Nitrates can interfere with iodine uptake by the thyroid gland
- Reproductive effects: Some studies link high nitrate exposure to adverse pregnancy outcomes
Who Is Most at Risk?
- Infants under 6 months (most vulnerable)
- Pregnant women
- Adults with reduced stomach acidity
- People with certain genetic conditions (G6PD deficiency)
- Homes near agricultural fields, feedlots, or failing septic systems
Nitrate Testing
- Cost: $15-$30 for nitrate analysis
- Frequency: Test annually, and additionally during pregnancy, a baby's first 6 months, after heavy rain in agricultural areas
- When to test: Spring and early summer (after fertilizer application and snowmelt)
- Standard: EPA MCL of 10 mg/L; ideal is below 5 mg/L
Nitrate Treatment
- Reverse osmosis: Most effective point-of-use treatment; removes 85-95% of nitrates. Cost: $200-$500 for under-sink units
- Ion exchange: Whole-house treatment using anion exchange resins. Cost: $1,500-$4,000
- Distillation: Effective but slow and energy-intensive. Cost: $150-$500 for countertop units
- Important: Water softeners, carbon filters, and boiling do NOT remove nitrates
Bacteria: The Immediate Threat
Types of Bacterial Contamination
Total Coliform Bacteria
- What it indicates: General bacterial contamination; coliform bacteria are naturally present in soil and are not necessarily dangerous themselves
- Standard: Zero (0) coliform per 100 mL is the EPA standard
- Significance: Positive test indicates a pathway for contamination to enter the well
E. coli (Fecal Coliform)
- What it indicates: Fecal contamination from human or animal waste
- Standard: Zero (0) E. coli per 100 mL
- Significance: Positive test means sewage or animal waste is reaching your water supply — immediate health risk
How Bacteria Enter Well Water
- Failing septic systems: The most common source for homes with both a well and septic
- Surface water infiltration: Cracked or improperly sealed well casings
- Flooding: Floodwater can introduce bacteria directly into wells
- Animal activity: Livestock or wildlife near the wellhead
- Well construction defects: Improperly grouted casing, missing well cap, or damaged sanitary seal
The proximity of your septic system to your well is a critical factor. Most states require a minimum 50-100 foot separation.
Health Effects
- Gastrointestinal illness: Nausea, vomiting, diarrhea, stomach cramps
- Dysentery: Severe bloody diarrhea from specific pathogens
- Hepatitis A: Liver inflammation from fecal contamination
- E. coli O157:H7: Can cause kidney failure, particularly in children and elderly
- Cryptosporidium and Giardia: Parasitic infections from animal or human waste
Bacteria Testing
- Cost: $25-$75 for total coliform and E. coli
- Frequency: At least annually, plus after any flood event, well repair, or change in taste/odor
- Method: Collect sample in a sterile container provided by the lab; deliver within 24 hours
- Results timeline: Typically 24-48 hours from a certified laboratory
Bacteria Treatment
- Shock chlorination: One-time treatment to disinfect the well. Cost: $100-$500 professionally
- Continuous chlorination: Automatic chlorine injection system. Cost: $1,500-$3,000
- UV disinfection: Ultraviolet light kills bacteria without chemicals. Cost: $500-$2,000
- Well repair: Fix the source of contamination — repair casing, seal gaps, improve grading around wellhead
Complete Well Water Testing Schedule
| Test | Frequency | Cost | Priority |
|---|---|---|---|
| Total coliform & E. coli | Annually | $25-$75 | Essential |
| Nitrates | Annually | $15-$30 | Essential |
| pH | Annually | $10-$15 | Recommended |
| Iron & manganese | Every 2-3 years | $30-$50 | Recommended |
| Hardness | Every 2-3 years | $15-$25 | Recommended |
| PFAS | Once (then every 2-3 years if near contamination) | $200-$500 | Situation-dependent |
| Arsenic | Every 3-5 years | $25-$50 | Region-dependent |
| Lead & copper | Every 3-5 years | $30-$60 | Recommended |
| VOCs (pesticides, solvents) | Every 5 years | $100-$300 | Region-dependent |
| Comprehensive panel | Every 5 years | $300-$600 | Recommended |
For more on testing frequency and methods, see our well water testing guide.
When to Test Immediately
Do not wait for your annual schedule if:
- Flooding has occurred in your area
- Well work (repair, pump replacement, casing work) was performed
- Water changes in color, taste, odor, or clarity
- Nearby contamination event (chemical spill, septic failure, construction)
- New baby in the household (test for nitrates and bacteria)
- Illness in the household that could be waterborne
- Property transfer (comprehensive testing recommended for all home sales)
Frequently Asked Questions
How do I know if my well water has PFAS?
The only way to know is through laboratory testing — home test kits do not detect PFAS. Contact a state-certified laboratory and request a PFAS panel. If you live near a military base, airport, industrial site, or landfill, testing is especially important. Some states now offer free or subsidized PFAS testing for private wells.
Is well water safe for babies?
Well water can be safe for babies if it tests negative for bacteria and has nitrate levels below 10 mg/L. However, you should test specifically before using well water for infant formula preparation. The EPA recommends testing for nitrates during pregnancy and a baby's first six months. If nitrate levels are elevated, use bottled water for formula until treatment is installed.
What should I do if my well tests positive for E. coli?
Stop drinking the water immediately. Use bottled water for drinking and cooking. Contact your local health department. Have a licensed well professional inspect and shock-chlorinate the well. Retest 1-2 weeks after treatment. If bacteria persist, the contamination source (such as a nearby failing septic system) must be identified and resolved.
Can I treat PFAS with a standard water filter?
Standard refrigerator filters and pitcher filters are not effective against PFAS. You need either a reverse osmosis (RO) system or a granular activated carbon (GAC) filter specifically certified for PFAS removal. Look for NSF/ANSI P473 certification, which specifically tests for PFAS reduction.
How close can a septic system be to a well?
Most states require a minimum of 50-100 feet between a septic tank and a well, and 100-200 feet between a drain field and a well. These setbacks are designed to prevent bacterial and nitrate contamination of the well water. However, geology and groundwater flow direction also matter — in some cases, even these distances may not be adequate.
-- The Well & Septic Hub Team