How to Remove Arsenic from Water

Posted by
John Woodard on February 02, 2024

Throughout history, arsenic has been famed for its lethal toxicity. From its use as poison in ancient times to its inclusion as an ingredient in pesticides and herbicides today, arsenic has always held and still holds a deadly connotation. It comes as no surprise, then, that arsenic-contaminated water is an issue that needs to be addressed. Below you can find information about the risks of arsenic, how to test if your water contains arsenic, and how to remove arsenic from your water.

What is arsenic?

Arsenic is a highly toxic metalloid present in groundwater around the world. Groundwater is contaminated by arsenic in its inorganic form through natural deposits and various forms of pollution. Pesticides, for example, can settle and leach into nearby groundwater. Factories release inorganic arsenic into the environment at excessive rates, and rainwater carries that arsenic down to groundwater. Wells near natural deposits, industrial production, mining, or farming are particularly susceptible to arsenic contamination. The 5 states with the highest levels of inorganic arsenic concentration in groundwater are California, Maine, Nevada, Arizona, and Illinois. States in the western, midwestern, and northeastern United States are most susceptible to arsenic contamination. According to the WHO, countries other than the United States with concerning levels of groundwater arsenic include Mexico, Chile, Argentina, China, India, and Bangladesh.

Is arsenic in my tap water?

Regardless of the source of your tap water, there is likely arsenic present to some extent. If you drink water from a well, you are likely at risk for some negative effects of arsenic exposure. Some city water may contain trace levels of arsenic, but most arsenic poisoning from water consumption stems from wells. While you may not experience acute arsenic poisoning from tap water, you may still have some long-term health problems from arsenic-contaminated water. Below you can find appropriate levels of arsenic for drinking and cooking, as well as information about arsenic in well water.

Learn more: Is tap water safe to drink?

Arsenic in drinking water

Arsenic has been detected in groundwater in all 48 contiguous states. No matter where in the United States you live, inorganic arsenic is likely present to some extent in your tap water. The EPA requires city water to contain fewer than 10 parts per billion (ppb) of arsenic. 10 ppb of arsenic in drinking water is considered safe for a lifetime of exposure. However, controversy surrounds the effects of long-term exposure to concentrations of 10 ppb or fewer. Some studies suggest that even miniscule doses of arsenic increases one’s risk for diabetes and cancer.

Arsenic in cooking water

Water used for cooking is considered safe by the Oregon Health Authority (OHA) in arsenic levels lower than 50 ppb. Pasta and rice dishes especially should not be cooked in water with higher than 50 ppb of arsenic because they absorb significant amounts of water in the cooking process. Soups and stews are also high risk when cooked with water with above 50 ppb of arsenic. For uses such as bathing and swimming, the OHA considers water safe with concentrations of 500 ppb of arsenic or fewer. Inorganic arsenic does not easily absorb into skin, so exposure to it is low risk if not consumed. Children may swallow water when bathing or swimming and should be supervised when dealing with water that is unsafe to ingest.

Arsenic in well water

The most dangerous concentrations of arsenic reside in well water. Since private wells are not monitored by a governing authority, well water can contain dangerous levels of arsenic. Inorganic arsenic can reach well water through natural deposits, industrial waste, and agricultural products such as pesticides and herbicides. In areas with industrial pollution, rainwater can pick up arsenic from the air and carry it down to groundwater, contaminating your well. Fertilizers, animal feed, and pesticides can also cause inorganic arsenic to leach into groundwater. Knowing the chemical composition of your well water is essential in living a healthy lifestyle. Fortunately, testing water for arsenic is a straightforward process.

Arsenic drinking water standards

The EPA standard for arsenic in drinking water is 10 parts per billion (ppb). Despite this standard, consuming water with even 10 ppb can be detrimental to health over an extended period. Filtering arsenic from your water may not be necessary at low enough concentrations. Ideally, however, drinking water contains no arsenic whatsoever. Private wells are not held accountable by the EPA, so private well owners should put filter systems in place to ensure all contaminants, not just arsenic, are removed.

Learn more: What is the best filter for well water?

How to test water for arsenic

Arsenic test kits are a quick and effective way to check your water for arsenic. These test kits are easy to use, and many provide results in just 12 minutes. First, you will mix your water with a tartaric acid reagent. Next, you will add an oxidizing reagent to the mixture to remove hydrogen sulfide interference. Finally, you will include a third reagent, zinc powder, to change the inorganic arsenic into arsine gas. The test strips inside the kit will then measure the levels of arsine gas in the water mixture. The results of these tests cannot distinguish between arsenic III and arsenic V. Arsenic III is much more toxic than arsenic V, and water containing arsenic must be pretreated by converting arsenic III to arsenic V. If your water contains more than 10 ppb of arsenic, assume it is arsenic III and pretreat accordingly.

Learn more: How to test water at home with a water test kit

Why do I need to remove arsenic from water?

In high enough doses, consuming inorganic arsenic is fatal. Ingesting arsenic in lower concentrations increases chances for both diabetes and cancer if consumed over a long period of time. The following symptoms are associated with arsenic poisoning:

  • Nausea
  • Vomiting
  • Diarrhea
  • Cramping
  • Sore throat
  • Numbness in extremities

If your water contains trace amounts of arsenic, you will likely not experience any of these symptoms, but your long-term health is still put at risk.

Learn more: Well water contamination and its symptoms

Can I cook with arsenic-contaminated water?

The safety threshold for arsenic in water is higher for cooking purposes than for drinking. While drinking water is considered safe at 10 ppb or fewer, water with concentrations of 50 ppb or fewer is considered safe for cooking by the Oregon Health Authority. What you cook factors into how safe cooking with arsenic-contaminated water is. Pasta, rice, oats, and herbs absorb water when boiled, making arsenic poisoning a greater threat with dishes containing these foods. Caution should also be exercised when making foods that are liquid-based, such as certain stews and soups.

While cooking is acceptable with arsenic levels between 10 and 50 ppb, making drinks out of water with these concentrations is a health hazard. Coffees, teas, and other water-based drinks should be made with water containing fewer than 10 ppb of arsenic.

Keep in mind that inorganic arsenic exposure is more dangerous to children than it is adults. For maximum safety, you should avoid cooking with water containing more than 35 ppb of arsenic. This includes water used for washing fruits and vegetables.

Do I need whole-house water treatment for arsenic?

Filtering arsenic from water in point-of-use sources where water will be consumed from is essential. While inorganic arsenic is toxic when it enters the body, it does not easily absorb through skin. For point-of-entry uses such as bathing and gardening, water with arsenic concentrations of fewer than 500 ppb is safe if not ingested. Keep in mind that children may swallow water while bathing, brushing their teeth, or swimming. If your water contains levels of arsenic above the safe drinking levels, children must be supervised to ensure they do not ingest toxic amounts of arsenic.

If arsenic is present in your water, other chemicals may be present as well. To know if point-of-entry filtration is necessary for your home, you will need to test for other contaminants.

How do I filter arsenic from well water?

Reverse osmosis is widely considered the most effective method of removing arsenic from well water. Reverse osmosis systems remove a high percentage of contaminants from water, including heavy metals, nitrates, sulfates, and many more. To preserve a reverse osmosis system’s lifespan when dealing with well water, other systems may need to be incorporated. Below you can find alternatives to reverse osmosis and how to incorporate different systems together to effectively filter well water.

Arsenic III vs Arsenic V

Arsenic presents itself in water in multiple forms, and its toxicity depends on which form it exists in. Inorganic arsenic is primarily found in two different oxidation levels, arsenic III(As3) and arsenic V(As5). Because of its high solubility in water, As3 is significantly more toxic than As5. If As3 is present in water, pretreatment via converting As3 to As5 allows more arsenic to be removed in the final treatment. The most common process of converting As3 to As5 involves oxidation by chlorine.

Best water filters for removing arsenic

Once the As3 is converted, you can remove a vast majority of arsenic from the water. The most effective treatments for arsenic in water are:

  • reverse osmosis.
  • distillation.
  • ion exchange.

Reverse osmosis

Reverse osmosis (RO) treats water by pushing pressured water through a semi-permeable membrane. This process removes sodium, chloride, copper, lead, arsenic, and many other contaminants. RO systems eliminate arsenic V at a higher rate than arsenic III, making pretreatment important for best results.

RO systems are typically point-of-use (POU) systems attached to a dedicated faucet. POU RO systems allow you to use filtered water for drinking, cooking, and making ice. These systems usually only produce about 2 to 3 ounces of water per minute but utilize a storage tank to allow you to access water at your convenience.

For arsenic-contaminated well water, point-of-entry (POE) RO systems are still a valuable option. POE RO systems allow you to use filtered water for every application in your house, such as bathing and gardening. In many cases, RO is the preferred method of removing As3 from water before it enters a house. While these systems are much more costly, they are well worth the price tag if your water contains dangerous amounts of arsenic.

Learn more about whole-house reverse osmosis solutions: Do I Need a Whole House Reverse Osmosis System?

Pros of reverse osmosis

  • RO systems effectively reduce As5 from water. Since point-of-use systems are acceptable for removing arsenic, RO systems are inexpensive compared to exclusively point-of-entry systems.
  • RO provides some of the best quality water available from a home water treatment system.

Cons of reverse osmosis

  • RO requires extensive pre-treatment to be successful. Sediment can diminish the efficacy of the RO system’s pre-filters, and chemicals can damage the RO membrane. RO systems are ideal for pre-treated city water and are not designed to treat raw, untreated well water. Knowing the chemistry of your water is essential in placing the appropriate pre-filtration systems in place.
  • RO strips water of its mineral content. This reduction results in a flat and bland taste unless the system contains a remineralization cartridge.

Learn more: What is a Reverse Osmosis System and How Does It Work? | 5 of the Best Reverse Osmosis Systems


Distillers work by heating water, collecting the resulting steam, and cooling the steam down to a liquid state. When water is boiled, contaminants with a higher boiling point than water are left behind because they cannot evaporate. The evaporated water is then cooled and drips into a collection container. Distillers remove soluble minerals and heavy metals such as lead, arsenic, and mercury.

Unlike IX and RO systems, distillers are neither point-of-use nor point-of-entry systems. Rather, home distillers are countertop systems that must be manually filled. In homes, distillers are typically only used for drinking and cooking because hooking a distiller to a faucet or to your house’s water supply is not possible.

Pros of distillation

  • Distillers remove waterborne pathogens and heavy metals. As a result, drinking distilled water lessens the likelihood of illness contracted from drinking water.
  • A distiller is excellent for eliminating toxic elements such as inorganic arsenic. For applications where toxic contaminants are present in water, distillation is a valid method of water purification.

Cons of distillation

  • Distillers cannot be hooked directly to a water source. Rather, they are manually filled, and can only produce small quantities of water at a time.
  • Since they require a heated energy source, distillers cost more to operate and are less environmentally friendly than other methods. How much you plan on using a distiller determines the practicality of the increased operating cost.
  • Removing chemicals with similar boiling points to water can be difficult with distillers. Precise pressure and temperature are required to remove as much contamination as possible.
  • Distillers require regular maintenance to ensure efficiency and effectiveness. Minerals collect in the boiling chamber over time, and, if not cleaned, will affect a distiller’s performance.
  • Like reverse osmosis, distillation removes minerals and reduces oxygen in water. Distilled water, as a result, has a flat taste.

Learn more: What is a Water Distiller and How Does it Work? | Is Distilled Water Safe to Drink?

Ion exchange

Ion exchange (IX) is a process used in water softening and deionization to eliminate unwanted contaminants in water. IX systems that eliminate inorganic arsenic use an anion exchange resin that removes most of the arsenic from water. Water is placed under pressure and passes through multiple layers of resin beads that exchange ions in the contaminants with those that are not toxic in water. Once the resin is saturated, a brine made of salt or chlorine, depending on the charge of the counterions, rinses out the contaminants and regenerates the resin beads.

IX systems are more effective at removing As5 than As3, making pretreatment essential in effectively treating your water. Well water is often exposed to metals, causing the water’s pH to rise. IX filters are not as effective on alkaline water, so IX is not the best choice for well water without proper pre-treatment in place.

Pros of ion exchange

  • IX systems are typically whole-house systems. While whole-house systems are not completely necessary for arsenic removal, they may be needed to protect from other contaminants. Point-of-entry systems also protect from water that is accidentally ingested. For example, water that is swallowed while bathing or brushing your teeth is treated with a whole-house system.
  • In addition to treating an entire house, IX systems require little maintenance. These units must be stocked with salt or chlorine occasionally but require little to no maintenance otherwise.

Cons of ion exchange

  • IX systems do not remove particles or bacteria from water, so they are best paired with other filtration systems that reduce sediment and grime that can clog an IX system. IX systems also have high initial costs, especially considering they are best paired with other units and are typically point-of-entry systems.
  • In the unlikely event of a valve failure, it may be possible for some of the captured As5 to be released into the treated water.
  • IX with anion resin also lowers the pH of water, making it more corrosive. If your water travels through metal plumbing after treatment, you may need a neutralizer to treat the water directly following the ion exchange.

Does boiling water remove arsenic?

No, boiling water does not remove arsenic. Since water is lost in the form of steam during the boiling process, arsenic concentrations will grow the longer the water is boiled.

Is arsenic in bottled water?

Certain brands of bottled water may contain arsenic. A study by Consumer Reports shows that some brands of bottled water may have arsenic contamination at dangerous levels. Researching how a brand of bottled water is filtered and where the water is sourced from helps determine if water contains safe levels of arsenic.


If you have any further questions about which filtration method is right for you, please don’t hesitate to contact our experts.

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