Arsenic occurs naturally in rocks and soil, water, air, and plants and animals. Approximately 90 percent of industrial arsenic in the United States is currently used as a wood preservative, but arsenic is also used in paints, dyes, metals, drugs, soaps, and semi-conductors. Agricultural applications, mining, and smelting also contribute to arsenic releases in the environment.
Ground water sources of drinking water tend to have higher levels of arsenic than surface water sources. Western states have more systems with arsenic levels greater than 10 ppb. Parts of the Midwest and New England have some systems whose current arsenic levels are greater than 10 ppb, but more systems with arsenic levels that range from 2-10 ppb.