Here's the unsettling thing about arsenic: it isn't a pollution story. Nobody dumped it. In most affected wells, arsenic leaches naturally out of the bedrock the well is drilled through — which means pristine, remote, "nobody around for miles" wells test positive all the time. USGS surveys estimate that roughly 1 in 10 private wells in the U.S. exceeds the federal arsenic limit in hotspot regions, and about 2 million Americans may be drinking water above the standard without knowing it.
You cannot taste it, smell it, or see it at any concentration that matters. The only way to know is a lab test — and if you've never run one, this is the article that should convince you to.
What the Numbers Mean
The EPA limit is 10 parts per billion (ppb, or µg/L). Note the billion — arsenic is regulated a thousand times more tightly than nitrate, because it's a confirmed human carcinogen at chronic low doses.
- Under 10 ppb: Meets the federal standard. (New Hampshire and New Jersey use a stricter 5 ppb — health agencies increasingly consider "as low as reasonably achievable" the right target.)
- 10–50 ppb: Above standard. Stop using for drinking and cooking; treatment or bottled water for ingestion. No panic — arsenic risk is chronic, built over years, not acute.
- Over 50 ppb: Treat urgently and consider retesting to confirm before major decisions.
Chronic exposure is linked to skin, bladder, and lung cancers, cardiovascular disease, and developmental effects in children. Because harm accumulates silently over decades, the danger isn't this glass of water — it's the 20,000 glasses after it.
Hotspot regions: New England (granite bedrock), the upper Midwest (glacial aquifers in Minnesota, Wisconsin, Michigan), the Southwest and interior West (Nevada, Arizona, California's Central Valley), and parts of the Texas Panhandle. But arsenic ignores county lines — the only map that matters is your lab report.
Test with a certified lab, not a color strip — at 10 ppb, strips are guesswork. The Tap Score Advanced Well Water Test covers arsenic alongside the full heavy-metal panel, and critically reports arsenic speciation matters — ask for arsenic III vs. arsenic V if your first result comes back high, because the split determines which treatment works.
Why Boiling and Carbon Don't Work
Same story as nitrate: arsenic is a dissolved inorganic. Boiling concentrates it. Carbon pitcher filters, fridge filters, and standard whole-house carbon do essentially nothing. Softeners don't touch it. Shock chlorination is irrelevant. If a salesman offers you a "whole-house arsenic carbon filter," walk away.
Treatment That Works
1. Point-of-use reverse osmosis (the default answer). An arsenic-rated under-sink RO system removes 90%+ of arsenic V for a few hundred dollars. Like nitrate, arsenic only harms you when ingested — skin contact and showering are fine — so treating the kitchen tap covers the actual exposure. One critical wrinkle: RO removes arsenic V well but arsenic III poorly. If your speciation shows significant As-III (common in the Midwest's low-oxygen aquifers), you need an oxidation step (often a small chlorination stage) ahead of the membrane, or a system designed for combined As-III/As-V.
2. Adsorptive media (whole-house or point-of-use). Iron-oxide adsorption filters (granular ferric oxide/hydroxide media) grab both arsenic species and can treat the whole house. Cartridges exhaust silently — no taste change, no warning — so replacement must run on schedule and treated-water retests are non-negotiable.
3. Anion exchange works for As-V in low-sulfate water but is the fussiest option; get professional sizing.
Whatever you install: retest the treated water 2–4 weeks after installation, then every 6–12 months. Arsenic treatment failing is invisible in every way except on a lab report.
Your Action Plan
- If you've never tested for arsenic: order the test this week. Once is mandatory for every well, everywhere. It's naturally occurring — no nearby polluter required.
- Result over 10 ppb: Switch drinking/cooking water to bottled today; request speciation; install RO (plus oxidation if As-III) or adsorptive media.
- Verify: Retest treated water within a month of installation.
- Forever after: Retest treated water every 6–12 months and replace membranes/media on schedule — this is the entire game with arsenic.
Arsenic management is pure calendar discipline: media that expires invisibly, retests that slip, results that get lost in an email inbox. Put it all in the WellKept app — log the lab numbers, set the media replacement reminder, and let it nag you for the retest. With a contaminant you can't sense, your log is your safety system.
Frequently Asked Questions
How do I know if my well water has arsenic? Only a laboratory test can tell you — arsenic has no taste, odor, or color at any relevant concentration. Every private well should be lab-tested for arsenic at least once, because it occurs naturally in bedrock and does not require any nearby pollution source.
Is it safe to shower in water with arsenic? Yes. Arsenic is not absorbed through intact skin in meaningful amounts and doesn't volatilize into shower steam the way some contaminants do. The exposure that matters is drinking and cooking, which is why an under-sink reverse osmosis system at the kitchen tap addresses the real risk.
Does reverse osmosis remove arsenic from well water? Yes — a quality RO system removes 90%+ of arsenic V, the common form in oxygenated water. Arsenic III, common in low-oxygen Midwest aquifers, passes RO membranes much more easily and needs an oxidation step first. Ask your lab for speciation before buying equipment.
What level of arsenic is safe in well water? The EPA standard is 10 ppb (micrograms per liter); New Hampshire and New Jersey enforce 5 ppb. Because arsenic is a carcinogen with no true "safe" threshold, health agencies recommend getting as low as reasonably achievable — under 5 ppb is a good practical target for treated water.
Can I boil arsenic out of well water? No — boiling evaporates water and leaves arsenic behind, increasing its concentration. Carbon pitcher filters and water softeners are also ineffective. Only reverse osmosis, adsorptive iron-oxide media, anion exchange, or distillation remove arsenic.