Comprehensive Water Treatment Process

  • Untreated water is drawn from the upper-Tualatin River at the Spring Hill Intake, near Forest Grove.
  • Untreated water is then pumped to the rapid mix 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 sedimentation basin.
  • After settling, polymer is added in the flume to help the filters remove particles that make it out of the sedimentation basins.
  • The water is then filtered through layers of anthracite coal and silica sand. As suspended particles are removed, turbidity disappears, and clean 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.
  • Caustic soda (sodium hydroxide) is added to adjust the final pH and alkalinity to reduce pipe corrosion.
  • The treated – or “finished” water – is then temporarily stored in an underground water reservoir, called a Clearwell.
  • Finally, finished water is pumped either to the Fernhill Reservoirs or directly into the three large water transmission pipelines.
  • From there, water travels into a network of storage reservoirs and partner’s water distribution lines before arriving ready to drink at customer’s taps.