Is your private well water safe?
Over 43 million Americans drink from private wells that the EPA does not regulate or test. We map USGS models of arsenic and nitrate risk across 3,103 counties and 49 states — then help you pick the right reverse-osmosis system to treat it.
Filter selector tool
Reverse-Osmosis & Filter Selector
Pick what you're concerned about and your household size — get the right system, the exact cartridge schedule, and the yearly cost.
Recommended tier
Under-sink Reverse Osmosis (5-stage)
Reverse osmosis is required for your water
Carbon pitchers and faucet filters do not reliably remove arsenic. A multi-stage reverse-osmosis system is the EPA-recognized treatment that brings these below the federal limit at your drinking-water tap.
APEC ROES-50 5-Stage Reverse Osmosis System
★ 4.7Check Price on AmazonLower-cost alternative
Waterdrop 3-Stage Under-Sink Filter
~$55
Lower-cost under-sink carbon for PFAS/taste — pair with RO for arsenic/nitrate.
Check Price on Amazon →Your replacement-cartridge schedule
An RO system only keeps working if you change the cartridges. For a 3-person household, here's the schedule and the running cost:
| Cartridge | Replace | Cost |
|---|---|---|
| Sediment + 2 carbon pre-filters | every 6–12 months | ~$40 / set |
| RO membrane | every 2–4 years | ~$60 |
| Post-carbon polishing filter | every 12 months | ~$20 |
Not sure what's in your well?
Private wells aren't regulated by the EPA, so no one tests them for you. Test first, then filter for what you actually find.
Shop Well Water Test Kits →We may earn a commission from Amazon when you buy through these links, at no extra cost to you. Product recommendations are based on treatment type and contaminant, not paid placement.
This is a modeled probability for the area, not a measurement of your well. USGS statistical models estimate how many private wells in this area are likely to exceed the federal limit — they cannot tell you what is in your water. Two neighbors can have very different results. The only way to know your well is to test it.
Highest modeled nitrate risk (private wells, by state)
All states →Share of each state's private-well population with modeled nitrate above the 10 mg/L EPA limit. Source: USGS (Ransom et al., 2022).
~17,900 well residents above the nitrate limit
~144,000 well residents above the nitrate limit
~43,300 well residents above the nitrate limit
~28,300 well residents above the nitrate limit
~12,600 well residents above the nitrate limit
~85,900 well residents above the nitrate limit
Counties with the most private-well arsenic exposure
More →Estimated population on private wells with modeled arsenic above 10 µg/L. Source: USGS (Lombard et al., 2021).
~22,522
well residents above the arsenic limit
Rockingham County, NH~21,388
well residents above the arsenic limit
Mecklenburg County, NC~19,183
well residents above the arsenic limit
Penobscot County, ME~18,708
well residents above the arsenic limit
Los Angeles County, CA~17,244
well residents above the arsenic limit
Hillsborough County, NH~17,240
well residents above the arsenic limit
Kennebec County, ME~15,277
well residents above the arsenic limit
Canyon County, ID~14,043
well residents above the arsenic limit