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Portland Water Bureau

From forest to faucet, we deliver the best drinking water in the world.


1120 SW Fifth Ave, Suite 600, Portland, OR 97204

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Source Water Treatment

diagram of the water treatment process

Portland’s water system delivers water from two high-quality sources: the Bull Run Watershed and Columbia South Shore Well Field.

Water from the Bull Run Watershed is not filtered. Portland meets stringent requirements for remaining an unfiltered water system by restricting access to the watershed and having a watershed protection program.

Water from the Columbia South Shore Well Field is used to meet peak water demand during hot summer months. It is also used as an emergency source of supply when the Bull Run is not available. 


Portland’s drinking water is treated to produce high-quality drinking water to meet all state and federal drinking water regulations. Treatment is a three-step process:

1. Disinfection: chlorine is added at the source to disinfect the water. Chlorine is a strong disinfectant that kills bacteria as it travels through the pipes from the source to the Lusted Hill Treatment Facility.

2. Chloramination/Disinfectant Stabilization: At the Lusted Hill treatment facility, aqueous ammonia is added, which bonds with chlorine to form chloramines. Chloramines are a disinfectant that stays in water longer than chlorine. Using chloramines ensures that disinfection remains adequate throughout the entire distribution system while reducing the formation of disinfection by-products.

3. pH Adjustment: sodium hydroxide is added to increase the pH of the water to reduce corrosion of  lead and copper from plumbing systems. The target pH range for treated drinking water is 7.8 to 8.0.


Water from the Bull Run or groundwater source is not filtered. The Bull Run water meets the filtration avoidance criteria of the Surface Water Treatment Rule. The State of Oregon approved Portland’s compliance with these criteria in 1992. Portland continues to meet these criteria on an ongoing basis.


Portland does not treat drinking water for Cryptosporidium. In 2006, the EPA adopted the Long Term 2 (LT2) Enhanced Surface Water Treatment Rule. This rule also applies to Portland and builds on the Surface Water Treatment Rule. Portland does not treat its drinking water for Cryptosporidium due to a treatment variance issued by the Oregon Health Authority.

 The two major requirements of the LT2 rule that apply to Portland include:

Visit the LT2 page for more information, including history and monitoring reports.