Arsenic in well water is a genuine health concern — it's colorless, tasteless, and odorless. Here's how to test for it and the filter systems that actually remove it.
Arsenic naturally leaches into groundwater from rock formations in many parts of the US — particularly the Southwest, Pacific Northwest, New England, and Midwest. If you have a private well in an at-risk area, testing is essential. Many homeowners don't know they have arsenic because you can't see, smell, or taste it.
Check the USGS groundwater arsenic maps or your state's environmental agency for local data. If you're in a high-risk area, test regardless of whether you've had issues.
| Mail-in lab test | Most accurate — $30–$80. Use a certified lab. Submit water sample by mail, receive results in 5–10 days. |
| Arsenic test strips | Quick field test — $15–$25. Lower accuracy but useful for initial screening. Detectable down to ~10 PPB. |
| Local health department | Many offer low-cost or free testing for private well owners. Check your county health department. |
Not all filters remove arsenic. Carbon filters, UV systems, and standard sediment filters do NOT remove arsenic. The systems that work:
| Reverse osmosis (RO) | Most effective — 90–99% removal. Point-of-use under-sink RO is the most practical approach for drinking water. |
| Adsorptive media (iron oxide, activated alumina) | Whole house arsenic removal. Requires periodic media replacement. Effective for arsenic removal at the whole-house level. |
| Anion exchange | Effective for arsenate (As V). Less effective for arsenite (As III) — water often needs oxidation pretreatment. |
| Distillation | 100% effective but slow, uses energy, and only practical for small volumes of drinking water. |
For most households, an under-sink RO system at the kitchen tap is the most practical arsenic solution. It handles drinking and cooking water where arsenic exposure is most significant. NSF 58-certified RO systems are specifically tested for arsenic removal.
If whole-house arsenic removal is required (for bathing exposure, which is lower risk than ingestion), a whole-house adsorptive media system is the appropriate solution.
Arsenic occurs in two forms in water: arsenate (As V) and arsenite (As III). As V is more common and most treatment systems target it effectively. As III is harder to remove — if your water contains primarily As III, pre-oxidation (adding chlorine or peroxide upstream) converts it to As V, making it treatable by standard methods.
Your lab test results will specify which form is present if you request speciation testing.