You cannot see, smell, or taste arsenicArsenicA toxic element found naturally in bedrock that dissolves into groundwater. Odorless and tasteless, making testing the only way to detect it.EPA MCL: 10 ppb (0.01 mg/L)Learn more → (a toxic element found in bedrock). The only way to know if it is in your well water is to test.
Arsenic is a serious health concern. The EPA sets the limit at 10 ppbPPB (Parts Per Billion)A unit of concentration equivalent to micrograms per liter (µg/L). Used for trace contaminants like arsenic, lead, and PFAS where even tiny amounts matter.Learn more → (parts per billion)[2]. If your test shows arsenic above this level, you need treatment.
Quick Answer
A point-of-use reverse osmosisReverse Osmosis (RO)A treatment method that forces water through a semipermeable membrane, removing up to 99% of dissolved contaminants including arsenic, lead, fluoride, nitrates, and PFAS.Learn more → (RO) system (a filter that pushes water through a membrane) removes up to 99% of arsenic. It costs under $300 and installs under your kitchen sink. For whole-house treatment, an adsorptive media system costs $1,500–$3,000.
What Is Arsenic and Why Is It in Your Well?
Arsenic is a natural element in certain rock formations. As groundwater flows through these rocks, it dissolves arsenic. Think of it like invisible rust seeping from stone into water[3].
It is most common in the Southwest, New England, upper Midwest, and Northern Plains. But it can appear anywhere. Geology determines risk, not geography alone.
Arsenic exists in two forms in groundwater:
- Arsenic III (arsenite): Harder to remove. Needs oxidation before filtration.
- Arsenic V (arsenate): Easier to remove. Most filters target this form.
A good lab test will report both forms[6].
Have your water test results? Get a treatment plan based on your exact numbers.
Analyze My Water TestHealth Risks of Arsenic in Well Water
Arsenic is a known carcinogen. Long-term exposure through drinking water is linked to cancers of the skin, bladder, lungs, kidney, and liver[5].
It also causes skin changes, numbness in hands and feet, and stomach problems. Children face higher risk because they drink more water per pound of body weight[4].
This is a YMYL (your money, your life) contaminant. Do not delay testing or treatment. Always use a certified lab — not a DIY test strip — for arsenic[8]. See our well water testing guide for how to collect a sample and how often to retest.
What Your Arsenic Level Means
| Level | Status | What It Means | What to Do |
|---|---|---|---|
| 0–5 ppb | Low Risk | Below most health thresholds. | Retest every 3 years. Consider RO for drinking water. |
| 5–10 ppb | Caution | Below EPA limit but above some state limits. | Install RO for drinking water. Retest annually. |
| 10–50 ppb | Exceeds EPA Limit | Above the legal MCLMCL (Maximum Contaminant Level)The highest level of a contaminant allowed in public drinking water, set by the EPA. Private wells are not regulated by MCLs, but they serve as the best available safety benchmarks.Learn more → (maximum contaminant level). | Install RO immediately. Consider whole-house system. |
| 50+ ppb | Urgent | Well above safe levels. Significant health risk. | Switch to bottled water now. Install treatment ASAP. |
Some states set stricter limits than the EPA. New Jersey and New Hampshire both set their limit at 5 ppb[9][13]. California's public health goal is even lower — 0.004 ppb — though its enforceable limit remains 10 ppb. Check your state's standard.
Arsenic Risk by Region: Where It's Worst
Arsenic is not spread evenly. Your risk depends on local geology. Nationally, about 7% of private wells exceed 10 ppb. But in some regions, that number is more than double[11].
| Region | Key States | Risk Level | Geology / Why |
|---|---|---|---|
| Southwest | Arizona, Nevada, New Mexico | Highest | Volcanic rock and desert basin sediments. ~16% of wells exceed 10 ppb. |
| Northern New England | Maine, New Hampshire | High | Granite bedrock leaches arsenic. 25–30% of NH private wells exceed 5 ppb. |
| Upper Midwest | Michigan, Wisconsin, Minnesota | Moderate–High | Glacial aquifer deposits with arsenic-bearing minerals. |
| Northern Plains | Montana, North Dakota, South Dakota | Moderate–High | Organic-rich shale and alluvial sediments release arsenic. |
| Central Valley, CA | California | Moderate | Alluvial fan sediments in agricultural regions. |
| Southeast / Piedmont | NC, VA, SC, GA | Lower | Crystalline rock and coastal plain. Risk pockets near old mine sites. |
| Gulf Coast | FL, TX (coastal), LA | Lower | Sandy aquifers with less arsenic-bearing rock. Still test — local pockets exist. |
Even in "lower-risk" areas, individual wells can test high. Arsenic varies well to well, not just region to region. A neighbor's clean test does not mean yours is safe[3].
If you live in a high-risk state, check your state-specific guide: North Carolina, Virginia, Florida, Texas, or South Carolina.
How to Test for Arsenic in Well Water
Do not use DIY test strips for arsenic. They lack the accuracy needed for health decisions at the ppb level. Use a state-certified lab[8].
Cost: $20–$40 for an arsenic-only test. $100–$200 for a full well water panel through a mail-in service like Tap Score.
Ask the lab to report arsenic III and arsenic V separately. This determines which treatment system works best. Retest every 1–3 years depending on your level[1].
How to Find a Certified Lab Near You
The EPA will not test your private well water for you. You need a state-certified lab. Here is how to find one[12]:
- Use the EPA's lab directory. Go to the EPA's certified lab page and select your state. Each state maintains its own list of labs approved for drinking water testing.
- Call your county health department. Many counties offer low-cost arsenic testing or can refer you to a certified lab in your area. Some states subsidize arsenic testing in high-risk counties.
- Use a mail-in service. Companies like Tap Score and National Testing Laboratories ship you a sampling kit. You collect the sample, mail it back, and get results in 5–10 business days. A full well water panel (including arsenic) costs $100–$200.
When you contact the lab, ask these questions:
- Are you certified for arsenic testing in my state?
- Do you report arsenic III and arsenic V separately? (This matters for treatment.)
- What is your detection limit? (Should be 1 ppb or lower for arsenic.)
- How should I collect the sample? (Some labs want a "first-draw" sample; others want a flushed sample.)
Do not rely on DIY test strips for arsenic. Most strips measure in 10 ppb increments. That means a strip showing "0" could actually be 9 ppb — just below the EPA limit. A lab test gives you exact numbers to the ppb.
Already have your results? Enter them in our Water Test Interpreter for a full treatment plan. Need help reading the report? See our guide on how to read a water test.
2 Ways to Remove Arsenic from Well Water
Point-of-Use Reverse Osmosis (Best for Drinking Water)
A reverse osmosisReverse Osmosis (RO)A treatment method that forces water through a semipermeable membrane, removing up to 99% of dissolved contaminants including arsenic, lead, fluoride, nitrates, and PFAS.Learn more → (RO) system pushes water through a very fine membrane. It blocks up to 99% of arsenic, plus lead, fluoride, nitrates, and PFASPFAS (Per- and Polyfluoroalkyl Substances)Synthetic chemicals used in nonstick coatings, firefighting foam, and food packaging. Known as 'forever chemicals' because they do not break down in the environment.EPA MCL (2024): 4 ppt for PFOA and PFOS individuallyLearn more → (forever chemicals)[7].
It installs under your kitchen sink. You get a separate faucet for filtered drinking and cooking water.
Cost: $150–$400. Filter replacements run $50–$80 per year.
This is the most affordable arsenic solution. It protects your drinking water right away.
See our best reverse osmosis systems
Whole-House Adsorptive Media System
For whole-house coverage, an adsorptive media system uses iron-based media. The media grabs arsenic as water flows through the tank. Think of it like a sponge designed to absorb only arsenic[6].
This treats all water in your home — showers, laundry, and every tap. Media needs replacement every 3–5 years.
Cost: $1,500–$3,000 installed. Media replacement runs $300–$500.
See our best reverse osmosis systems
Important: Arsenic III Requires Pre-Treatment
Most filters remove arsenic V well but struggle with arsenic III. If your test shows arsenic III, you need an oxidation step first. A chlorine injection or oxidizing pre-filter converts III to V before the main filter[6].
DIY vs. Professional Installation
An under-sink RO system is a straightforward DIY project. Most kits include everything you need. Plan for 1–2 hours.
Whole-house adsorptive media systems need plumbing work. Professional installation is recommended. The stakes are higher with a health contaminant — proper setup matters.
What to Do Next
Step 1: Get a certified lab test for arsenic. Do not rely on DIY strips for this contaminant.
Step 2: If above 10 ppb, install an under-sink RO system right away. This protects your drinking water while you research whole-house options.
Step 3: Enter your full test results in our Water Test Interpreter for a complete treatment plan.
Frequently Asked Questions
What level of arsenic in well water is dangerous?
The EPA limit is 10 ppb[2]. Any amount above this requires treatment. Some experts recommend treating above 5 ppb, especially for children.
How do I test for arsenic in well water?
Use a certified lab test. Not a DIY strip. Cost: $20–$40 for arsenic alone, or $100–$200 for a full panel. Ask for arsenic III and V reported separately.
What filter removes arsenic from well water?
A reverse osmosis system removes up to 99% for under $300. It installs under your kitchen sink. For whole-house coverage, use an adsorptive media system ($1,500–$3,000).
Can you boil arsenic out of water?
No. Boiling does not remove arsenic. It actually concentrates it by evaporating water. You need a filter like reverse osmosis or adsorptive media.
Which states have the most arsenic in well water?
The highest levels occur in Arizona, Nevada, New Mexico, Maine, New Hampshire, Michigan, and Wisconsin[3]. In the Southwest, about 16% of wells exceed 10 ppb. In New Hampshire, 25–30% of private wells exceed 5 ppb. Arsenic comes from natural bedrock, so it varies by geology.
How do I find a certified lab to test for arsenic?
Go to the EPA's certified lab directory and select your state[12]. You can also call your county health department for a local referral. Mail-in services like Tap Score ship you a kit and return results in 5–10 business days. Always use a state-certified lab — not a DIY test strip — for arsenic.
Does arsenic in well water affect bathing and showering?
Arsenic is not absorbed well through skin. The main risk is drinking or cooking with arsenic-contaminated water. Bathing and showering are generally safe, even at levels above 10 ppb. That is why a point-of-use RO system at your kitchen sink is usually enough.
Can arsenic levels in my well change over time?
Yes. Arsenic levels shift with seasonal water table changes, drought, and heavy pumping from nearby wells[11]. A well that tested safe one year may exceed 10 ppb the next. The EPA recommends retesting every 1–3 years. Test annually if you have ever tested above 5 ppb.
References
- U.S. EPA. "Arsenic in Drinking Water." Ground Water and Drinking Water, 2024. https://www.epa.gov/ground-water-and-drinking-water
- U.S. EPA. "National Primary Drinking Water Regulations: Arsenic." 40 CFR Part 141, 2024. https://www.epa.gov/sdwa
- U.S. Geological Survey. "Arsenic in Ground Water of the United States." NAWQA Program, 2023. https://www.usgs.gov/mission-areas/water-resources
- World Health Organization. "Arsenic in Drinking-Water." Background Document, 2022. https://www.who.int
- National Cancer Institute. "Arsenic Exposure and Cancer Risk." NIH, 2023. https://www.cancer.gov
- Water Quality Association. "Arsenic Fact Sheet." Technical Resources, 2024. https://wqa.org
- NSF International. "NSF/ANSI 53: Drinking Water Treatment Units — Health Effects." 2024. https://www.nsf.org
- Penn State Extension. "Arsenic in Private Water Systems." College of Agricultural Sciences, 2023.
- New Hampshire DES. "Arsenic in New Hampshire Well Water." Environmental Fact Sheet, 2023.
- Maine CDC. "Arsenic in Private Well Water." Division of Environmental Health, 2023.
- U.S. Geological Survey. "Machine Learning Models of Arsenic in Private Wells Throughout the Conterminous United States." Environmental Science & Technology, 2020. https://pubs.usgs.gov/publication/70219045
- U.S. EPA. "Contact Information for Certification Programs and Certified Laboratories for Drinking Water." 2024. https://www.epa.gov/dwlabcert/contact-information-certification-programs-and-certified-laboratories-drinking-water
- New Jersey Department of Environmental Protection. "Arsenic in Drinking Water." Safe Drinking Water Act Rules, 2023.