Whole House Filtration for Private Well Owners

The unregulated reality of private wells

EPA's Safe Drinking Water Act regulates public water systems serving 25 or more people. Private wells fall outside this regulatory framework. There is no annual CCR. There is no required testing schedule. There is no automatic notification when contamination occurs. The homeowner is solely responsible for testing, treatment, and ongoing maintenance.

This is more responsibility than many well owners realise. State Departments of Health publish guidance, and several state Cooperative Extension Services offer subsidised testing, but the basic obligation rests with the homeowner. CDC's Guidelines for Testing Well Water is the standard reference.

Step 1: Annual testing

CDC recommends every private well be tested annually for four parameters at minimum:

• Total coliform bacteria - indicator of contamination pathway
• Nitrate (as nitrate-nitrogen) - agricultural runoff, methemoglobinemia risk for infants
• Total dissolved solids (TDS) - general mineral content
• pH - corrosion potential

Regional add-ons depend on local geology and land use. Arsenic in much of the western and northeastern U.S. Radon in northeastern and Rocky Mountain states. Pesticides where the well is downhill from agricultural land. Iron, manganese, and hardness almost everywhere. PFAS near AFFF source areas and industrial discharge. Test through a state-certified laboratory; home test kits flag obvious issues but are not suitable for treatment-system specification. See water testing.

Step 2: Map contaminants to treatment train

Different test results lead to different train configurations. The order of stages matters: sediment first to protect downstream stages, oxidation before any RO or anion exchange, UV at the end after the water has been polished.

Configuration 1: Low contaminant load

Test results show only hardness above 7 GPG; total coliform negative; nitrate within limits; no iron or manganese; arsenic within limits.

• Spin-down sediment 50 micron
• Depth sediment 5 micron
• Ion-exchange softener (NSF/ANSI 44)

No chemical treatment, no UV. Annual testing catches changes early.

Configuration 2: Iron and hardness

Test results show iron above 0.3 mg/L and hardness above 7 GPG; total coliform negative.

• Spin-down sediment 50 micron
• Oxidising iron filter (air injection or birm media)
• Depth sediment 5 micron
• Ion-exchange softener (downstream of iron - never upstream)

Iron above 0.3 mg/L fouls softener resin and shortens its life dramatically. Iron filtration belongs upstream of softening. See our iron page.

Configuration 3: Bacteria positive

Test results show total coliform positive (or worse, E. coli positive) on any sample.

• Investigate well integrity (sanitary cap, casing, surrounding area)
• Shock-chlorinate the well per state DOH instructions
• Re-test after shock chlorination
• If contamination recurs, install permanent treatment:
• Spin-down sediment 50 micron
• Iron filter if iron present (precedes UV)
• Depth sediment 5 micron (UV pretreatment)
• UV disinfection at 40 mJ/cm² (EPA UV Disinfection Guidance Manual)
• Softener if hardness present (downstream of UV is fine)

Configuration 4: Arsenic positive

Test results show arsenic above 5 to 10 ppb. Determine arsenic species (V or III) before specifying treatment.

• Spin-down sediment 50 micron
• If arsenic III dominant: oxidation stage (chlorine injection or potassium permanganate) to convert to arsenic V
• For low-level (less than 50 ppb) arsenic: iron-based adsorption media or whole-house anion exchange
• For higher arsenic concentrations or co-occurring contaminants: point-of-use reverse osmosis at the kitchen sink (NSF/ANSI 58 arsenic reduction claim)

Configuration 5: Nitrate above 10 mg/L

Test results show nitrate above the EPA MCL of 10 mg/L (as N). Particularly concerning for households with infants on formula.

• Do not use the water for infant formula until treated
• POU RO at the kitchen sink - NSF/ANSI 58 with nitrate reduction claim - is the standard residential intervention
• Whole-house anion exchange (nitrate-selective resin) for whole-home treatment if needed
• Investigate source: agricultural runoff, septic system proximity, fertiliser application

See our microbiological/nitrate page.

Configuration 6: The full multi-contaminant well

Some wells test positive for iron, manganese, bacteria, hardness, and (sometimes) arsenic. The train sequence matters; an out-of-order configuration can cause downstream failures.

• Spin-down sediment 50 micron
• Oxidation stage (chlorine injection if pathogens or arsenic III present, otherwise air injection for iron)
• Iron and manganese filter (birm or manganese greensand)
• Depth sediment 5 micron
• GAC carbon (removes residual injected oxidant)
• Ion-exchange softener
• UV disinfection at 40 mJ/cm²
• POU RO at the kitchen sink for arsenic, nitrate, or PFAS where present

What private wells often need that city water does not

• UV disinfection: Essentially mandatory if total coliform has ever been detected. EPA recognises UV at 40 mJ/cm² and 254 nm as effective. See UV page.
• Iron treatment: Many wells exceed the 0.3 mg/L Secondary MCL. Standard configuration is oxidation followed by filtration through specialty media. See arsenic and iron page.
• Higher sediment loading: Wells frequently produce more sediment than municipal water, particularly during low-water seasons or after pump cycling.
• pH adjustment: Some wells produce aggressive low-pH water that corrodes copper plumbing and leaches metals. Calcite or soda-ash neutralising filters address this.
• Ongoing testing discipline: Annual testing is the homeowner's responsibility. Without it, contamination can persist undetected for years.

Related: CDC well testing protocol, Coliform and nitrate, Arsenic and iron, UV disinfection.