Over a two year period, the U.S. Environmental Protection Agency, Drinking Water Research Division (EPA-DWRD), and two New England water utilities evaluated the water quality from redwood slat tower aerators. Samples of aerator influent and aerator effluent were analyzed for several volatile organic compounds, some of which are being considered for possible regulatory action (1). The two principal organics in the waters were trichloroethylene and cis-1,2-dichloroethylene; the sum of the concentrations ranged from 9 to 300 micrograms per liter micrograms/L). In addition, fourteen inorganic compounds (seven of which have maximum contaminant levels (2)) and three microbiological parameters (standard plate count, total coliforms, and Legionella) were routinely monitored. Precipitation of iron and the subsequent buildup of sludge on the distribution plate inside the aerators at one site decreased the efficiency for removing volatile organic compounds. These experiences underscore the need for routine attention and maintenance on any treatment process.