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Arsenic in Water
Arsenic is a naturally occurring mineral that can silently infiltrate your water supply, posing serious health risks without any noticeable taste or smell. Whether you're drinking from a public water system or a private well, arsenic contamination is something every American should be aware of. According to the Environmental Working Group (EWG), an estimated 70 million Americans in 48 states are exposed to arsenic in drinking water at levels considered unsafe by scientific standards. Another 2.7 million people relying on private wells may also be drinking water with dangerously high arsenic levels. Let’s dive into the science, the risks, and what you can do to protect yourself and your family.
Arsenic is a toxic element found naturally in soil and rock, but it also enters the water supply through human activities like mining, agriculture, and the use of fossil fuels. It seeps from rock formations into groundwater, which supplies both municipal water systems and private wells.
Western U.S. states tend to have the highest levels of arsenic in water, but no region is completely safe — arsenic contamination has been detected in all 50 states.
Health Effects of Arsenic in Drinking Water
The Environmental Protection Agency (EPA) and World Health Organization (WHO) have both classified arsenic as a known human carcinogen. Long-term exposure, even at low levels, has been linked to:
Bladder, lung, and skin cancer
Kidney, liver, and prostate cancers
Skin lesions
Cardiovascular disease
Immune system harm
Developmental problems in children
Cognitive impairments
Increased toxicity for smokers
A 2023 EPA draft report revealed arsenic is 30 times more toxic than previously estimated. Yet the legal U.S. limit remains at 10 parts per billion (ppb), a level the EPA’s own analysis says could lead to up to 600 cancer cases per million people drinking water at that concentration over a lifetime.
Arsenic iii & arsenic v
Arsenic in drinking water exists primarily in two forms: arsenic (III), also known as arsenite, and arsenic (V), or arsenate. The key difference lies in their chemical structure and behavior in water. Arsenic (V) is the oxidized form and is more commonly found in surface water, while arsenic (III) is the reduced form and typically occurs in groundwater. From a health standpoint, both forms are toxic and linked to serious health risks, including cancer, cardiovascular disease, and developmental issues. However, arsenic (III) is considered more dangerous because it is more readily absorbed by the body and is harder to remove through conventional water treatment methods.
The removal of arsenic (V) is generally more straightforward, as it tends to bind better with filtration media like activated alumina, iron-based media, and certain ion exchange resins. In contrast, arsenic (III) poses a greater challenge due to its uncharged, more mobile form, which doesn’t readily bond with typical filtration materials. As a result, effective removal of arsenic (III) often requires an oxidation step to first convert it into arsenic (V), followed by filtration. This distinction is important when evaluating water filtration systems, especially for homes that rely on well water—because a system that only removes arsenic (V) may not provide adequate protection if arsenic (III) is present.
Symptoms of Arsenic Poisoning
Chronic arsenic exposure may not produce immediate symptoms, but over time it can cause:
Fatigue or weakness
Skin darkening or lesions
Numbness in hands and feet
Abdominal pain
Nausea and vomiting
Diarrhea
Memory or concentration issues
Frequent respiratory infections
If you rely on well water or live in a region known for arsenic contamination, testing is crucial, even if you feel fine.
How to Test for Arsenic in Water
If you’re on a public water supply, start by checking your local utility’s water quality report or consult the EWG Tap Water Database to see if arsenic is a known issue in your area. If you use well water, contact your local health department for testing resources. You can also go online and use a company called Tap Score. Arsenic levels can vary widely, even from house to house, so don’t rely solely on regional data.
The EPA must lower the federal arsenic limit in drinking water to reflect the current understanding of its toxicity. At the same time, the federal government and local utilities should invest in improved treatment technology and public education campaigns to reduce exposure.
Until then, the responsibility falls on individuals to test and treat their water and be mindful of food sources.
Sources:
Baris et al. (2016) – Elevated Bladder Cancer in Northern New England: The Role of Drinking Water and Arsenic – Journal of the National Cancer Institute, 108(9).
Environmental Protection Agency – Drinking Water Arsenic Rule History
Naujokas et al. (2013) – The Broad Scope of Health Effects from Chronic Arsenic Exposure – Environmental Health Perspectives, 121(3):295–302.
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