For 8 months, the Seattle Water Department conducted a corrosion treatment pilot plant study, obtaining data on the treatment of Tolt River water with lime and sodium carbonate. Pipe loop tests were conducted to determine the appropriate chemical start-up procedures for two full-scale corrosion treatment facilities; to document the effectiveness of the corrosion treatment program in suppressing corrosion, metal leaching and tuberculation in older galvanized steel premise plumbing systems; to document the bacterial effects of the corrosion treatment program on water quality; and to anticipate any possible customer problems caused by implementation of the corrosion treatment program. The study monitored the effects of simulated corrosion treatment start-up on chemical and microbial water quality from an old galvanized plumbing system. Standing water samples collected after treatment start-up displayed increased iron deposits, organic debris and bacterial populations compared to untreated standing water samples. Zinc leaching was reduced during treatment from pH 6 to pH 7 and increased from pH 7 to pH 8. Iron leaching was found to increase by approximately 38% during treatment start-up, while copper and lead leaching were reduced by 53% and 57%, respectively. Corrosion treatment also resulted in a reduction of approximately 32% in the tuberculation rate.