Well Water: Complete Homeowner's Guide
Complete guide to well water filtration: what to test for, how to read results, and the full filter stack for bacteria, iron, arsenic, and PFAS. Backed by Tap Score lab data.
Why Well Water Is Fundamentally Different from City Water
The EPA Safe Drinking Water Act does not apply to private wells serving fewer than 25 people. No federal agency tests your well, monitors it, or requires you to treat it. You are entirely responsible for your own water quality. Approximately 43 million Americans drink from private wells — and the vast majority have never had a comprehensive test done.
Private well contamination patterns differ from city water: geological sources (arsenic, radon, hardness, iron, manganese) are common because groundwater contacts minerals for years before reaching your aquifer. Agricultural contamination (nitrates, pesticides, herbicides) affects wells in farming regions — the contaminants travel through soil over months or years, so contamination from a neighbor's field may not appear in your water for a decade. Bacterial contamination from septic systems, flooding, or surface water infiltration can develop quickly and is life-threatening at high concentrations.
Well Water Contaminants: Frequency, Risk Level, and Treatment
| Contaminant | Prevalence | Health Risk | Detectable? | Treatment |
|---|---|---|---|---|
| Coliform / E. coli | Common (15-20% of wells tested) | Critical — can be fatal | No odor/taste/color | UV sterilizer (NSF 55 Class A) + disinfection |
| Nitrates | Very common in agricultural areas | High for infants/pregnant | No odor/taste/color | RO system (removes 88-92%) |
| Iron | Very common in groundwater | Low health risk; major staining/taste issue | Orange/red staining, metallic taste | Iron filter (oxidation/filtration) or softener |
| Hardness (calcium/magnesium) | Common throughout US | Low; scale damage to appliances | Scale on fixtures, soap scum | Water softener (ion exchange) |
| Arsenic | Regional (New England, Rockies, Southwest) | High — carcinogen (bladder, lung cancer) | No odor/taste/color | NSF 53 arsenic media or RO |
| Hydrogen Sulfide | Common in shallow wells, coastal areas | Low at typical levels; irritating | Rotten egg odor | Activated carbon or oxidizing filter |
| Manganese | Common in older wells | Neurological effects at high levels (>0.3 mg/L) | Black/brown staining, bitter taste | Iron/manganese filter or softener |
| PFAS | Detected in 45% of US water sources | High — carcinogen, endocrine disruption | No odor/taste/color | NSF P473 filter or RO |
| Radon | Common in granitic regions | High — lung cancer risk from inhalation | No odor/taste/color | Aeration or granular activated carbon |
The Well Water Treatment Stack: In the Right Order
Treatment order matters. Installing a UV system downstream of a sediment problem renders it ineffective — turbid water blocks UV light from reaching bacteria. Installing a softener before an iron filter destroys the softener resin. The correct sequence:
Sediment Pre-Filter (5–50 micron)
Removes particles that damage or clog downstream equipment. 20-micron for most wells; 5-micron before UV systems. Replace every 2–6 months depending on sediment load.
$20-60/year in cartridges
Iron / Manganese Filter (if needed)
Oxidizes dissolved iron/manganese so it can be mechanically filtered. Must come before softener — iron destroys softener resin. Skip if iron <0.3 mg/L.
$699-1,200 installed; $30-50/year in media
Water Softener (if hardness >120 mg/L)
Ion exchange removes calcium and magnesium, preventing scale. Must come after iron removal. Salt consumption: 8-12 lbs/week for typical household.
$800-1,500 installed; $120-200/year in salt
UV Sterilizer (if bacteria risk)
NSF 55 Class A UV at 40 mJ/cm² or higher (Viqua D4 Premium, $370) disinfects bacteria and viruses. Only effective in clear, post-sediment water. Required for any detected coliform or E. coli.
$370 installed; $60/year lamp replacement
Chemical Filtration (point-of-use)
RO under-sink for nitrates, arsenic, PFAS, and dissolved TDS. Carbon block for chlorine or taste issues. Applied at the point of use — kitchen tap — rather than whole-house to preserve cost efficiency.
$150-450; $60-120/year in filters
Recommended Systems by Test Result
Test result: E. coli or coliform detected
Do not drink until treated. Install Viqua D4 Premium UV ($370, NSF 55 Class A) after a sediment pre-filter. Retest 2 weeks after installation. Also identify and eliminate the contamination source (failed septic, surface water intrusion).
Test result: Nitrates above 5 mg/L
Install RO under-sink (APEC ROES-50, $220, NSF 58 — removes 91% of nitrates). For whole-house nitrate treatment (uncommon need): anion exchange system. Do not use water for infant formula or during pregnancy above 5 mg/L.
Test result: Iron above 0.3 mg/L / Manganese above 0.05 mg/L
Install SpringWell Iron Filter WS-FE1 ($699 whole-house). For moderate iron (0.3-3 mg/L): whole-house carbon block may suffice temporarily. Above 3 mg/L: oxidizing filter or air injection system required.
Test result: Arsenic above 5 ppb
Install point-of-use RO (APEC ROES-50, $220, removes 95%+ arsenic) or NSF 53-certified arsenic-specific media filter. For whole-house arsenic: adsorptive media (greensand plus, activated alumina) — more expensive but addresses all taps.
Test result: PFAS detected at any level
Install NSF P473-certified filter (AquaTru Classic countertop RO, $349) or under-sink RO (APEC ROES-50, $220). PFAS is not covered by a separate P473 certification when using a generic RO — confirm the specific system has tested PFAS reduction.
Test Before You Buy Any Treatment Equipment