Arsenic in Drinking Water: What You Need to Know
Arsenic is a naturally occurring element found in the earth's crust. It dissolves into groundwater through rock erosion and enters surface water through industrial runoff. The problem is that arsenic is completely invisible: no taste, no odor, no color. The only way to know it's in your water is to test for it.
The EPA has set the maximum contaminant level (MCL) for arsenic at 10 parts per billion (ppb). That sounds protective, but many health researchers argue it isn't low enough. Studies have documented health effects at concentrations below the legal limit, which means "compliant" water isn't necessarily safe water.
Private well water carries the highest risk. Municipal systems are required to test and treat for arsenic, but private wells have no federal regulation. If you're on well water, nobody is testing for arsenic unless you do it yourself.
Standard carbon filters, the kind found in most pitcher filters and refrigerator filters, don't remove arsenic in any meaningful amount. Specialized filtration is required.
Key Takeaways
Health Risks of Arsenic Exposure
The International Agency for Research on Cancer (IARC) classifies arsenic as a Group 1 carcinogen, the highest classification reserved for substances with sufficient evidence of causing cancer in humans. This puts arsenic in the same category as asbestos and tobacco smoke. Source: American Cancer Society
Chronic exposure to arsenic, even at levels below the 10 ppb EPA limit, has been linked to a range of serious health conditions:
- Skin, lung, bladder, and kidney cancers
- Skin changes including pigmentation disorders and lesions
- Cardiovascular disease
- Neurological effects, particularly in children
- Endocrine disruption
Children are especially vulnerable. Research has associated early-life arsenic exposure with cognitive development issues and reduced immune function. Pregnant women face additional risks, as arsenic crosses the placental barrier.
Arsenic exposure effects develop gradually over years. You won't feel sick immediately. That's what makes it dangerous: by the time symptoms appear, long-term damage may already be done.
The CDC's Agency for Toxic Substances and Disease Registry (ATSDR) ranks arsenic as the number one substance on its priority list of hazardous substances. Not second. Not fifth. First.
How Arsenic Gets into Your Water
Arsenic enters drinking water through two main pathways, and understanding which one affects your area helps you assess your risk level.
Natural Erosion
Arsenic-bearing rocks and minerals dissolve slowly into groundwater over time. This is the most common pathway, and it affects large regions of the United States. The Southwest, Midwest, New England, and parts of the Pacific Northwest all have naturally elevated arsenic in groundwater. If you live in one of these areas and rely on a well, your odds of arsenic contamination go up significantly.
Industrial Contamination
Mining operations, metal smelting, pesticide manufacturing, and historical use of arsenic-based wood preservatives have left behind contamination in soil and water sources across the country. Even in areas without naturally high arsenic levels, proximity to former industrial sites can mean elevated concentrations in local groundwater.
There's an important distinction between well water and city water. Municipal water systems are required to test for arsenic and treat it if levels exceed 10 ppb. But "treated" doesn't mean "zero." Your city water can legally contain up to 10 ppb of arsenic and still be considered compliant.
Private wells have no such requirement. They draw directly from groundwater with no treatment, no testing, and no reporting. The EPA recommends well owners test their water regularly, but compliance is voluntary. EPA: Protect Your Home's Water
How to Test for Arsenic in Your Water
You cannot see, smell, or taste arsenic in water. No home test strip on the market reliably detects it at the low concentrations that matter for health. A laboratory water test is the only way to know your arsenic level with confidence.
If you're on city water, start with your utility's Consumer Confidence Report (CCR). Every public water system is required to publish one annually, and it will list arsenic levels along with other contaminants. You can find yours through the EPA's CCR search tool.
If you're on well water, a professional lab test is the only option. The EPA recommends testing at least once per year, and more frequently if you're in a high-risk region or have had previous detections. Crystal Quest offers water testing kits that can be sent to a certified lab for analysis.
Test for both Arsenic III and Arsenic V if possible. They require different filtration approaches, and knowing which form is present helps you choose the right system.
Arsenic III vs Arsenic V: Why It Matters
Not all arsenic is the same. It exists in two primary forms in water, and the distinction between them determines which treatment method will actually work.
Arsenic III (arsenite) is the more toxic and more difficult form to remove. It carries a neutral electrical charge in water, which means most filtration media can't attract or bind to it effectively. Reverse osmosis alone only removes 60-80% of Arsenic III. That's a problem if your well water contains 50 ppb: even after RO treatment, you could still be above the EPA limit.
Arsenic V (arsenate) carries a negative charge, making it far more responsive to adsorption-based filtration. Iron-oxide media and RO systems handle Arsenic V with 95-99% effectiveness. If your water only contains Arsenic V, treatment is relatively straightforward.
The real challenge is Arsenic III, and the solution is pre-oxidation. By introducing an oxidizing agent before filtration, Arsenic III converts to Arsenic V. Once converted, it becomes easy to capture. Crystal Quest offers a chlorine pre-dosing system designed specifically for this conversion step.
If your water test shows high Arsenic III levels, a standalone filter may not be enough. Pre-oxidation before the filter converts Arsenic III to Arsenic V, which is much easier to remove.
This is why testing for both forms matters. A water test that only reports "total arsenic" doesn't tell you whether you need pre-oxidation or not. Speciated testing gives you the information you need to build the right system.
How to Remove Arsenic from Water
First, a quick list of what does not work:
- Standard carbon pitcher filters remove less than 20% of arsenic
- Sediment filters target particles, not dissolved contaminants
- Water softeners are designed for hardness minerals, not arsenic
- Boiling actually makes it worse by concentrating arsenic as water evaporates
Effective arsenic removal requires targeted technology. These methods actually work.
EagleOxide Iron-Oxide Media
Crystal Quest uses EagleOxide resin in its dedicated arsenic removal systems. This is an iron-oxide based adsorption media that binds to arsenic molecules as water passes through. It works on both Arsenic III and Arsenic V, though performance against Arsenic III improves significantly when paired with pre-oxidation.
Iron-oxide adsorption has a key advantage over other methods: it works at whole-house flow rates. You can treat every tap in your home, not just one faucet. The EagleOxide media is available as a standalone replacement cartridge or pre-installed in Crystal Quest arsenic filtration systems.
Reverse Osmosis
RO systems push water through a semi-permeable membrane that blocks most dissolved contaminants. For Arsenic V, removal rates reach 95-99%. For Arsenic III, expect 60-80% without pre-oxidation. Add a pre-oxidation step, and RO handles both forms at 95%+ removal.
RO is best suited for point-of-use applications. Most residential RO systems install under a kitchen sink and serve a single faucet. They produce purified drinking water but aren't designed to treat an entire household.
| Method | Arsenic III Removal | Arsenic V Removal |
|---|---|---|
| Standard Carbon | 10-20% | 10-30% |
| EagleOxide Media | 85-95% | 95-99% |
| Reverse Osmosis | 60-80% | 95-99% |
| Pre-Oxidation + RO | 95-99% | 98-99%+ |
Choosing the Right Arsenic Filter
Your choice depends on two things: whether you need whole-house protection or point-of-use drinking water, and whether your water contains Arsenic III, Arsenic V, or both.
For whole-house treatment, an iron-oxide media system treats every tap, shower, and appliance in your home. This is the right choice if your arsenic levels are high enough that you want protection beyond just drinking water.
For drinking water only, a countertop or under-sink system gives you treated water at the kitchen faucet. These systems are more affordable and easier to install, making them a good starting point if your arsenic levels are moderate.
If your test shows significant Arsenic III, plan on adding pre-oxidation to whichever system you choose. Without that conversion step, no single-stage filter will get you to the removal rates you need.
Frequently Asked Questions
How do I know if arsenic is in my water?
You can't detect arsenic by sight, taste, or smell. The only reliable method is a laboratory water test. If you're on city water, check your annual Consumer Confidence Report (CCR) for arsenic levels. If you're on a private well, send a water sample to a certified lab for analysis. Test at least once a year.
What level of arsenic in water is dangerous?
The EPA's legal limit is 10 ppb, but health effects have been documented at concentrations below that threshold. Arsenic is a Group 1 carcinogen, and many researchers argue there is no truly safe level of chronic exposure. If your water tests above zero, filtration is worth considering.
Do regular water filters remove arsenic?
No. Standard carbon filters, including those in pitchers and refrigerators, remove very little arsenic (10-30% at best). You need a filter specifically designed for arsenic removal, such as one using iron-oxide adsorption media or a reverse osmosis membrane.
What's the difference between Arsenic III and Arsenic V?
Arsenic III (arsenite) carries a neutral charge and is harder to remove with filtration. Arsenic V (arsenate) carries a negative charge and responds well to most arsenic filtration technologies. Pre-oxidation converts Arsenic III into Arsenic V, making it easier to filter.
Can you boil arsenic out of water?
No. Boiling water does not remove arsenic. It actually concentrates it. As water evaporates, the arsenic stays behind in a smaller volume of water, increasing the concentration. Never rely on boiling as a treatment for arsenic contamination.
Does reverse osmosis remove arsenic?
Reverse osmosis is highly effective against Arsenic V, removing 95-99%. It's less effective against Arsenic III, removing only 60-80%. Adding a pre-oxidation step before the RO membrane brings Arsenic III removal up to 95-99% as well.
