Arsenic in Drinking Water

Arsenic is a naturally occurring element found in rocks and soil throughout the Earth's crust. It enters drinking water primarily through the dissolution of natural mineral deposits as groundwater flows through arsenic-rich geological formations. This means that well water and groundwater-fed systems are often more affected than surface water supplies. Human activities also contribute: agricultural pesticides (many now banned), industrial processes, mining operations, and wood preservatives have all added arsenic to the environment.

Long-term exposure to arsenic in drinking water -- even at levels close to the current EPA standard of 10 parts per billion -- has been convincingly linked to increased risks of bladder, lung, skin, kidney, and liver cancers. Non-cancer effects include thickening and discoloration of the skin, cardiovascular disease, diabetes, and neurological problems. The World Health Organization has called arsenic in drinking water one of the most significant public health threats globally, and the EPA's MCLG of zero reflects the scientific consensus that no level is considered safe.

Arsenic contamination is especially common in the western United States, parts of the Midwest, and New England, where geological conditions naturally concentrate arsenic in groundwater. If you rely on a private well, testing is essential because private wells are not subject to EPA monitoring requirements. Even if you are on a public water system, older systems in high-arsenic areas may struggle to consistently meet the 10 ppb standard.