For 6 months, the Seattle Water Department conducted a corrosion treatment pilot plant study, obtaining data on the treatment of Tolt River water with lime/sodium carbonate, lime/sodium bicarbonate, and lime/bicarbonate/silicate. Continuous-flow pipe coupon tests were conducted to determine corrosion rates, penetration rates, and corrosion types for copper, galvanized steel and black steel pipes. Metal leaching tests were conducted using small diameter pipes. Research showed that using lime plus sodium carbonate, lime plus sodium bicarbonate, and lime plus bicarbonate plus silicate will significantly reduce corrosion in home plumbing systems. Based on this pilot study, lime plus sodium carbonate treatment is recommended for the Cedar River water supply at an average dosage of 1.7 mg/L CaO. This dose should achieve an average distribution system pH of 7.9 and an alkalinity of 18 mg/l CaCO3.