Arsenic is a naturally occurring element present in rocks and soil. As water passes through and over geologic formations it can dissolve arsenic. The result is that arsenic can be present in some water sources. Ingesting drinking water containing arsenic can cause adverse health effects. Most notably, arsenic is a known carcinogen, and long-term ingestion may increase the risk of cancer. Public water supplies must comply with the EPA standard of 10 ppb which became effective in January 2006 or must have obtained an extension. Management of a private drinking water well for arsenic is a decision made by the well owner and/or water user. Research is being conducted to identify effective, economical methods for arsenic removal and residual disposal. The treatment system or combination of systems that will be best for a given situation depends on several factors. Each individual private well owner/user needs to determine their willingness to accept risk, and work with professionals to manage the risk.