The JWC Water Treatment Plant is located in Forest Grove, Oregon. It operates 365-days per year, 24-hours a day. The plant was built in 1976, and has undergone multiple expansions. It is the largest conventional water treatment plant in Oregon, capable of producing up to 85 Million Gallons per Day (MGD).

The plant provides water to the Hillsboro Water Department’s in-town, upper-system, and wholesale customers, as well as to JWC partner agencies, including the cities of Hillsboro, Forest Grove, and Beaverton, and the Tualatin Valley Water District. The City of North Plains also received water from the JWC as a wholesale customer. 

Treatment Process

Before reaching the taps of the Hillsboro Water Department’s in-town customers, water undergoes comprehensive treatment overseen by state-licensed drinking water operators at the Water Treatment Plant:

• Untreated water is drawn from the upper-Tualatin River at the Spring Hill Intake, near Forest Grove.


• Untreated water is then pumped to a mixing tank where chlorine and alum are added. The chlorine serves as a disinfectant. The alum causes small particles to rapidly “floc” or adhere to one another, making them heavy enough to settle out of the water in a sediment basin.


• The water is then filtered through layers of anthracite coal and silica sand with the help of a filter aid polymer. As suspended particles are removed, turbidity disappears and clear water emerges. Removing turbidity through filtration is an effective way to protect against Cryptosporidium. 


• At this point, the lowest quantity necessary of chlorine is added. This kills harmful pathogens, such as bacteria and viruses, and keeps them from growing in Hillsboro’s more than 300-miles of water pipelines.


• The treated or “finished” water is then temporarily stored in an underground water reservoir called the clear well where Caustic Soda (sodium hydroxide) is added to adjust the final pH and alkalinity to reduce corrosion of lead. 


• Finally, finished water is pumped either to the Fernhill reservoirs or directly into the two large water transmission pipelines.


• From there, water travels into a network of storage reservoirs and distribution lines before safely arriving ready to drink at customers’ taps.

Learn more about this treatment process. 

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The Cherry Grove Slow Sand Filter Plant (SSFP) is located near the community of Cherry Grove, Oregon. It is capable of treating up to three MGD of water and provides water to the Hillsboro Water Department’s upper-system customers, along with the JWC Water Treatment Plant. The plant also provides water to some of the Hillsboro Water Department’s wholesale customers, the City of Gaston and the L.A. Water Cooperative.  

Treatment Process

The SSFP uses a highly effective form of treatment called slow sand filtration. This filtration process is one of the world’s oldest water treatment methods, and employs a biological process to clean the water.

The treatment process includes:

• Untreated river water is drawn from the upper-Tualatin River at the Haines Falls Intake, near the community of Cherry Grove.


• After going through screens, water travels through a pipe to a settling pond to remove silt, and make the water clearer.


• Water is then piped to the slow sand filters for treatment. In the filters, water slowly percolates by gravity through a bed of fine sand.


• The top layer of the filters is where most treatment takes place. It is called the “Schmutzdecke” and is formed by a community of organisms that naturally live in the water. This layer traps contaminants and pathogens that could be in the water — including silt, bacteria, Cryptosporidium, and Giardia.


• After passing through the filters, the water is chlorinated and final pH is adjusted to reduce corrosion of lead before being sent to customers through the water distribution system.

The Willamette Water Supply System Water Treatment is currently under construction. It is located in Sherwood, Oregon. When complete, it will provide water to the Cities of Hillsboro and Beaverton, and the Tualatin Valley Water District (TVWD). 

Treatment Process

• Untreated water is drawn from the mid-Willamette River in Wilsonville.


• Raw water is treated with a coagulant and enters the Actiflo process, which quickly removes turbidity and other contaminants.


• Ozone treatment kills microorganisms, prepares water for additional contaminant removal, and improves taste and odor.


• Granular activated carbon and sand filters remove cloudiness, organic material, and chemical contaminants.


• Ultra-violet (UV) light kills remaining microorganisms, including ones known to cause disease.


• Chlorine disinfection protects treated water as it travels through miles of pipes. Water is delivered to Hillsboro though new, large-scale, earthquake-resilient pipes.