The drinking water standard or maximum contaminant level (MCL) for arsenic is currently being re-evaluated by the US Environmental Protection Agency. The health risk associated with exposure to arsenic through consumption of drinking water is a primary concern in setting a new arsenic MCL. This paper examines the implications of arsenic chemistry, occurrence, and routes of exposure for risk assessment. In order to illustrate the relative importance of exposure through consumption of food and drinking water, the contribution of dietary intake to human exposure to inorganic arsenic was estimated as 2 μg/d. This estimate is based on a total dietary intake of arsenic of 40 μg/d and a 5% contribution of inorganic arsenic to the total dietary intake. This estimated value for dietary intake of inorganic arsenic (2 μg/d) is comparable to the exposure that would result from consumption of 2 l/d of drinking water containing 1 μg/l inorganic arsenic. At lower concentrations of arsenic in drinking water, daily intake of inorganic arsenic becomes increasingly dominated by the dietary contribution. Evaluation of standards for arsenic in drinking water should include careful consideration of exposure through other routes, particularly food consumption.