Effluent variability is one of the factors considered by industrial and municipal dischargers in setting wastewater treatment facility design goals. This paper develops variability data associated with the iron adsorption/coprecipitaton process, also known as the iron treatment process. This process can, under appropriate conditions, effectively reduce the concentration of certain metals found in aqueous discharges. Treatment facility designers and regulatory agencies can use the guidelines presented in this paper to estimate effluent variability in the most likely to-be-used iron treatment process configurations.