Arsenic is increasingly recognized as a serious threat to health and the environment. Inorganic As(III), considered one of the most toxic forms of the element, is generally present in reducing geochemical conditions. Removal of As(III) from water is often accomplished by oxidation to As(V), and subsequent removal by common water treatment processes. In the present study, As(III)) present in drinking, waste and industrial waters, was oxidized and precipitated as a scorodite-like mineral, FeAsO₄, by photochemical oxidation in the presence of air and iron. Waters were treated with low concentrations of ferrous ion, Fe²⁺, and air in an ultraviolet reaction chamber. Iron (II) apparently acts as a complexing agent and photoabsorber resulting in both Fe²⁺ and As³⁺ oxidation. This process provides an opportunity to greatly reduce the Iron dose needed to meet the new US-EPA MCL for As and offers the possibility of removal systems that rely on natural Fe as low a 300 ppb. The resultant Fe³⁺  and As⁵⁺ co-precipitate solid is removed from water by filtration. Removal of arsenic from western United States and Australian drinking water, a coal gasification sour stripper process water, and Chilean hot springs discharge is described. Ferric arsenate sludge retrieved from filter backwashing is rendered non-hazardous by fixing/stabilizing in special cement formulations. The resulting cement may be beneficially used in materials of construction or disposed of as a non-hazardous material. Examples of As residual stabilization are given.