Arsenic is a natural element that is widely distributed throughout the Earth's crust. It is often found naturally in groundwater, through erosion and weathering of soils, minerals, and ores. Arsenic compounds are used commercially and industrially in the manufacture of a variety of products and may enter drinking water sources directly from industrial effluents and indirectly from atmospheric deposition. This Guideline Technical Document reviews the health risks associated with arsenic in drinking water, focussing on inorganic forms of arsenic.