What is Arsenic* and Why Does It Matter?

Arsenic is a naturally occurring element found in rock and soil across much of the United States. As groundwater moves through these geological formations, it picks up arsenic along the way. Mining operations, agricultural pesticides, and industrial waste can also push arsenic into local water supplies. The result: 1,840 water systems across the country currently deliver water with arsenic levels above the EWG health guideline.

Most people associate arsenic with poison, and that instinct isn't wrong. Long-term exposure — even at low levels — is linked to serious health problems. The EPA and the International Agency for Research on Cancer (IARC) classify arsenic as a known human carcinogen. Regular consumption raises the risk of bladder, lung, and skin cancers. Beyond cancer, research published by the WHO connects chronic arsenic exposure to heart disease, diabetes, and developmental problems in children. At the highest levels detected in U.S. water systems — up to 15.6 parts per billion (ppb) — those risks become harder to ignore.

Here's where the numbers get important. The EPA's legal limit for arsenic in drinking water is 10 ppb. That standard sounds protective, but it was set in 2001 as a compromise between public health and the cost of water treatment — not based purely on what's safe. The EWG health guideline is far stricter: 0.004 ppb. That's the level associated with a 1-in-1-million increased cancer risk, which is the benchmark most public health scientists consider acceptable. The average arsenic level across affected systems is 1.532 ppb — well below the EPA's legal limit, but still more than 380 times above the EWG guideline. In other words, water that passes federal testing can still carry meaningful long-term risk.

Arsenic exposure isn't evenly distributed. Texas leads the country with 348 affected water systems, followed by Illinois (257), California (159), Kansas (147), and Iowa (73). This pattern reflects geology more than anything else. The Great Plains and Midwest sit on ancient geological formations rich in arsenic-bearing minerals. In Texas and Kansas, deep aquifers pull water through arsenic-laden rock before it ever reaches a treatment plant. California's affected systems are concentrated in agricultural regions of the Central Valley, where groundwater has been heavily drawn down over decades, concentrating naturally occurring contaminants. If your family relies on a private well in any of these states, it's worth knowing that private wells are not regulated by the EPA — testing is entirely your responsibility.

The good news is that arsenic is one of the contaminants that filtration handles well, as long as you're using the right technology. Standard pitcher filters and basic carbon filters do not remove arsenic effectively. Reverse osmosis (RO) systems are the gold standard here — they remove up to 99% of arsenic from drinking water. A quality under-sink RO system, like those Echo Water offers, filters water at the point of use, meaning the water coming out of your kitchen tap has gone through multiple stages of purification before it reaches your glass. If you're on a private well, whole-home treatment may also make sense depending on your water test results. The first step is always to test your water — knowing your actual arsenic level tells you exactly how much protection you need. From there, the right system can bring your water well below even the strictest health guidelines.

Regulatory Standards for Arsenic*

Cities With the Highest Arsenic* Levels

States Most Affected by Arsenic*

Frequently Asked Questions

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