Arsenic In Well Water: Detection, Health Risks & Removal
No taste. No smell. No color. No federal oversight for 43 million Americans on private wells. Here's what the science says, how to test, and the filtration proven to remove it.
Quick Answer: Can you remove arsenic from well water?
Yes. Reverse osmosis systems certified under NSF/ANSI Standard 58 remove 95–99% of arsenic. However, arsenic exists in two chemical forms. Arsenic III (As3+), the more toxic form common in deep groundwater, is electrically neutral and requires an oxidation pre-treatment step before RO can capture it.
What Is Arsenic & Why Is It In Your Well?
Arsenic is a naturally occurring metalloid (element 33) found in over 200 mineral forms in the earth's crust. It is not manufactured or industrial. Groundwater dissolves it from bedrock as it percolates through arsenic-bearing formations over centuries.
The concentration in your well depends entirely on the specific geology your well bore intersects. Two wells drilled a quarter mile apart can produce dramatically different arsenic levels if they penetrate different rock layers. A neighbor's clean test result tells you nothing about your own well.
How Arsenic Enters Your Well
Natural Geological Dissolution
Arsenopyrite, scorodite, and realgar minerals dissolve arsenic into groundwater over millennia. This is the dominant pathway for most wells with elevated arsenic. The rock beneath your property has been releasing arsenic into the aquifer for thousands of years.
Human-Caused Sources
Mining operations, historical lead arsenate pesticides (1890s–1940s), CCA pressure-treated lumber (phased out 2004), and industrial discharge create localized hotspots in shallow groundwater near contamination sites.
Depth does not equal safety. Deep bedrock aquifers with prolonged low-oxygen contact with arsenic-bearing minerals frequently contain the highest concentrations. Some of the worst contamination documented by USGS research occurs in deep bedrock wells in the Southwest and New England.
Arsenic Hotspots In The United States
Arsenic in groundwater is not distributed evenly across the country. If you live in one of these regions and rely on a private well, testing is not optional.
| Region | States | Primary Source | Risk Level |
|---|---|---|---|
| Southwest | AZ, NV, CA, NM | Arid basin-fill aquifers | Very High |
| Upper Midwest | WI, MN, MI, IA | Glacial deposits, sandstone | High |
| New England | ME, NH, VT | Granite & metamorphic bedrock | High |
| Great Plains | NE, SD, OK | High Plains aquifer system | Mod–High |
| Pacific NW | OR, WA | Volcanic geology, geothermal | Moderate |
| Southeast | FL, parts of GA | Phosphate deposits, old pesticides | Moderate |
Contamination is hyper-local. Regional maps indicate general risk, but your specific well depends on the exact rock your bore penetrates. Testing your individual well is the only way to know.
Arsenic III vs Arsenic V: Why It Matters For Filtration
Whether your filter actually works depends on which chemical form your well contains. This is the most important technical distinction in arsenic water treatment—one that most consumer resources skip entirely.
| Property | Arsenic III (Arsenite) | Arsenic V (Arsenate) |
|---|---|---|
| Chemical Form | As3+ (reduced) | As5+ (oxidized) |
| Charge in Water | Neutral | Negative |
| Toxicity | Higher | Lower |
| RO Removal (no oxidation) | 60–80% | 95–99% |
| RO Removal (with oxidation) | 95–99% | 95–99% |
| Typically Found In | Deep, low-oxygen groundwater | Oxygenated surface water, shallow wells |
The Solution: Oxidation Pre-Treatment
Oxidation converts As3+ → As5+ through one of several methods:
Without this step, your filter may remove only a fraction of detected arsenic. This is why arsenic speciation testing (not just total arsenic) is critical before selecting treatment.
The Health Risks Of Chronic Arsenic Exposure
Arsenic does not pass through your body quickly. It accumulates. After partial methylation in the liver, arsenic accumulates in skin, hair, nails, and internal organs over prolonged exposure. As documented by the WHO's arsenic fact sheet, contaminated drinking water is the most significant exposure source globally.
Documented Health Effects
Cancer (Group 1 IARC)
Bladder, lung, and skin cancer with dose-dependent risk. Strongest epidemiological association with bladder cancer. Elevated lung cancer risk documented even in non-smokers.
Cardiovascular Disease
Coronary heart disease, peripheral arterial disease (historically "blackfoot disease"), and hypertension. Arsenic damages vascular endothelium and promotes atherosclerotic plaque.
Neurological Damage
Peripheral neuropathy (tingling, numbness, pain) in adults. In children, associated with cognitive impairment and reduced IQ scores even at moderate exposure levels.
Skin, Metabolic & Developmental
Skin lesions and keratosis (5–15 years chronic). Type 2 diabetes. In children: developmental delays, reduced immune function, impaired growth. Reproductive effects including miscarriage.
The nature of the risk: The danger is not acute toxicity. It is chronic low-dose exposure over years and decades, a slow accumulation that may contribute to disease long before you know you've been exposed.
How To Test Your Well For Arsenic
Standard at-home test strips cannot detect arsenic at parts-per-billion concentrations. Detecting arsenic requires specialized lab analysis using EPA Method 200.8 with inductively coupled plasma mass spectrometry (ICP-MS).
Test Annually — Ideally Twice
Once in spring (after snowmelt recharge) and once in fall (lower water table = higher concentration). A well at 7 ppb in summer may reach 14 ppb after spring runoff.
Request Arsenic Speciation
Ask for total arsenic (combined ppb) plus speciation (As3+ and As5+ reported separately). If total is above 5 ppb, speciation is essential before selecting treatment.
Use A Professional Mail-In Lab Test
A certified mail-in test (Safe Home Ultimate or Tap Score Well Water Test) using EPA-approved ICP-MS methodology provides quantitative results accurate to 1 ppb or below—the only reliable method for arsenic.
How To Remove Arsenic From Well Water
What Does NOT Work
✕ Boiling water. Arsenic is non-volatile. Boiling concentrates it in the remaining liquid.
✕ Standard pitcher filters (Brita). Granular activated carbon is not designed or certified for arsenic removal.
The Complete Well Water Treatment Stack
Sediment Pre-Filter (5 micron)
Captures sand, silt, rust particles, and pipe scale. Protects all downstream equipment from fouling and abrasion.
Iron/Arsenic Oxidation Media Tank
Converts As3+ → As5+ through oxidation. Removes dissolved iron & manganese. This is the critical arsenic speciation conversion stage.
Activated Carbon Filter
Removes VOCs, pesticides, herbicides, taste & odor compounds. See best whole house carbon filters.
UV Purifier
Kills bacteria, viruses, and protozoa. Essential for any private well. See best UV purifiers for well water.
Under-Sink RO System
Final-stage purification at the drinking water tap for arsenic, heavy metals, nitrates, and all remaining dissolved contaminants. See best under-sink RO systems.
Recommended Products For Arsenic Removal
Our top picks based on independent testing, certifications, and real-world well water performance.
APEC ROES-50 Under-Sink RO System
The gold standard for arsenic-certified drinking water purification. Pair with upstream oxidation for wells containing As3+.
View on AmazoniSpring WGB32B 3-Stage Whole House
Provides the pre-treatment foundation that arsenic-specific downstream systems require. Clean, pre-filtered water ensures downstream arsenic media and UV operate at peak effectiveness.
View on AmazonViqua VH410 Whole House UV System
UV sterilization does not remove arsenic, but it is a non-negotiable component of any private well treatment stack for 99.99% biological protection with zero chemical addition.
View on AmazonArsenic Removal By Technology
Frequently Asked Questions
Chronic exposure typically produces no symptoms for years. The earliest visible signs are skin changes—darkened or lightened patches and thickened skin on palms/soles (keratosis)—developing over 5–15 years. Other symptoms include persistent fatigue, digestive issues, and peripheral neuropathy. Arsenic exposure is best identified through water testing, not symptom observation.
No. Arsenic is non-volatile—it does not evaporate. Boiling actually concentrates arsenic by reducing water volume. The only effective methods are reverse osmosis (NSF 58), iron-based adsorptive media, and specialized ion exchange resins, often preceded by oxidation pre-treatment for As3+.
No. Standard Brita pitchers use granular activated carbon—not designed, tested, or certified for arsenic. Removing arsenic requires an RO membrane (NSF 58 certified) or specialized iron-based adsorptive media. No standard consumer pitcher filter is effective.
The EPA MCL is 10 ppb for public water. New Jersey set 5 ppb. Both EPA and WHO acknowledge cancer risk exists below 10 ppb with chronic exposure. The National Research Council concluded 10 ppb does not fully protect against lifetime cancer risk. Many professionals recommend treatment at any detectable level, especially for children and pregnant women.
For drinking water: an under-sink RO certified under NSF 58 such as the APEC ROES-50. For whole-house: iron-based adsorptive media (Bayoxide E33). If your well contains significant As3+, add an oxidation pre-treatment step before either technology to convert arsenite to arsenate.
Yes, in specific geological regions. In parts of Arizona, Nevada, and New Hampshire, 20%+ of tested private wells exceed 10 ppb. Contamination is hyper-local—your well may be affected even if a neighbor's is not. The only way to know is certified lab testing.
At minimum once per year. Ideally twice: spring (post-snowmelt) and fall (lower water table). Also retest after changes in taste/color/odor, nearby construction, flooding, or well modification. Arsenic concentrations can shift seasonally.
Home test strips cannot reliably detect arsenic at ppb concentrations. Use a professional mail-in lab (Safe Home Ultimate or Tap Score). Request both total arsenic and speciation (As3+ and As5+) to determine the correct treatment approach.