What You Need to Know About Arsenic in Drinking Water in 2026

Long-term exposure to arsenic in drinking water is linked to cancers of the bladder, lung, and skin, along with several other serious health effects. 

Despite that, arsenic receives far less public attention than contaminants like lead or PFAS, largely because arsenic contamination comes from the natural geology (not industrial pollution or older plumbing infrastructure). As a result, it disproportionately impacts private wells, which are not subject to the same regulatory testing requirements as public water supplies. 

Quick Summary

• What is arsenic?: Arsenic is a naturally occurring, but toxic, element found in bedrock in some regions, and it can contaminate groundwater.  
• How does it contaminate water?: Arsenic generally contaminates drinking water through water coming into contact with arsenic-containing natural geologic deposits. 
• What are the health risks with arsenic contamination?: Long-term exposure to arsenic in drinking water has been linked to cancers of the bladder, lung, and skin, along with cardiovascular disease and diabetes. 
• What you can do: If your home uses a private well, testing is the first step. If treatment is needed, look for systems that carry NSF/ANSI Standards for arsenic reduction. 

What Is Arsenic?

Arsenic is a naturally occurring element found in rocks, soils, and groundwater.  

Scientists usually focus on two oxidation states of arsenic when talking about drinking water: arsenite [As(III)] and arsenate [As(V)]. These are sometimes referred to as trivalent arsenic and pentavalent arsenic, respectively.  

In municipal water systems that use chlorine as a disinfectant, arsenic is typically present as easier to filter As(V) because chlorine readily converts As(III) to As(V).  In private wells, the ratio of As(III) to As(V) depends on other biogeochemical factors like oxygen levels, pH, and microbial activity.   

Why You Should Care About Arsenic Levels in Drinking Water 

Long-term exposure to high levels of arsenic in drinking water has been linked to a number of different kinds of cancers, as well as heart disease and diabetes. A recent study by Columbia University and NYU shows that lowering arsenic in drinking water saves lives, even for people who have been exposed for decades.  

It’s important to note that arsenic often goes unnoticed because it doesn’t make water taste or smell bad.  This is yet another example of why testing and filtration are so critical, even if nothing “seems” wrong with your water. 

How Does Arsenic Get Into Drinking Water? 

Unlike contaminants that come from manmade chemicals or outdated plumbing components, arsenic contaminates drinking water because bedrock in some parts of the country contains arsenic. 

Because arsenic comes from geology, arsenic levels in drinking water follow regional patterns. In the United States, elevated arsenic levels in groundwater are most common in parts of the west, midwest, northeast, and some of the Atlantic southeast coastal states. 

One thing to understand is that even in regions with high arsenic in the bedrock, individual wells can have different arsenic concentrations. 

USGS data shows high concentrations of arsenic throughout the west, midwest, northeast, and some of the Atlantic southeast coastal states.

Who Is Most at Risk of Arsenic Contamination in Drinking Water? 

While arsenic can contaminate municipal groundwater sources, the 43 million people in the United States who get their drinking water from private wells are most at risk.  This is for two main reasons: 

• Testing: Private wells are not regulated by the federal or state government, so private wells often go untested for arsenic.  Many standard testing protocols neglect to test arsenic, which is a major oversight. 
• Treatment: Because municipal water supplies are regulated by the Safe Drinking Water act, municipalities are required to ensure that tap water levels remain below 10 parts per billion (ppb).  While there are known health risks below the 10ppb regulatory limit, there’s at least some protection. 

The USGS estimates that roughly 2.1 million people using domestic wells in the United States may be drinking water with arsenic concentrations above the federal drinking water standard. That makes arsenic one of the more important hidden risks in private well water. 

How Is Arsenic Regulated in Drinking Water? 

The EPA regulates arsenic at the federal level and has set an enforceable limit for public water systems at 10 ppb, as well as an unenforceable health-based goal at 0 ppb. 

Drinking water regulations are developed by balancing a contaminant’s health risks against the municipal cost and feasibility of treatment.  In this case, an enforceable Maximum Contaminant Level (MCL) of 10 ppb was determined more feasible than the 0 ppb health-based goal. 

A recent study by the EPA’s January 2025 IRIS review reinforces this point. The results show that 10 ppb of arsenic was associated with an increased risk of developing bladder and lung cancers, as well as ischemic heart disease and diabetes.    

How to Reduce Exposure to Arsenic In Drinking Water 

If you are on municipal water, the best place to begin is the local Consumer Confidence Report (CCR). Water utilities are required to publish this report annually, and it lists the concentrations of regulated contaminants that were detected in the system during the previous year.  

How to Test Arsenic in Drinking Water 

If you are on a private well, you are responsible for all testing, because private wells are unregulated.  Reliable arsenic testing is best done by ordering a test kit and having it analyzed by an accredited laboratory, as test strips are not accurate.  

Some states have free or subsidized testing programs for private well owners if the cost of testing is of concern.  We recommend that private well owners who live in regions with high levels of arsenic test their water for arsenic every 2-3 years.  

How to Filter Arsenic From Drinking Water  

If arsenic is present in your water, it must be addressed via filtration, as boiling does not remove heavy metals. 

Both whole house and point of use filters, such as under sink water filters, can be effective.  But it’s critical when evaluating products to ensure the presence of an NSF/ANSI standard 53 or 58 certification for arsenic reduction. These certifications ensure that the system has been tested to reduce arsenic, are structurally sound, and do not leach other harmful chemicals into water.  

Want to learn more about filtering arsenic from your home's water? Hydroviv's Water Experts are available to answer more questions through live chat.