Seattle Public Utilities (SPU) provides drinking water to 1.3 million people inthe metropolitan Seattle area from 2 surface water supplies, the Tolt and CedarRivers. For over 100 years, one of the primary objectives of Seattle's drinkingwater program has been to provide the highest possible level of source waterprotection. This high level of source water protection and the resulting rawwater quality has allowed Seattle's supplies to remain unfiltered. In the late1980s and throughout the 1990s, in response to changing drinking waterregulations and issues unique to Seattle's surface supplies, SPU has beendeveloping improved water treatment for both sources. The treatment improvementstrategies reflect the exceptional source protection. This paper will discuss Seattle's source protection and treatment programs and the resulting publichealth protection improvement and financial benefits that have accrued to SPU'scustomers. Includes figures.