Water Treatment Recommendation

A panel of national experts in drinking water treatment and public health recommended in June 2010 that the cities of Tigard and Lake Oswego pursue conventional filtration plus ozone treatment to best protect public health in the long term. 

The Lake Oswego Tigard Water Partnership plans to upgrade and expand Lake Oswego’s existing water treatment plant to serve both communities.  A 2007 engineering report* concluded that the current direct filtration treatment process must be converted to reliably produce top quality drinking water.

The expert panel validated the 2007 report results.  The panel confirmed the quality of raw water is very good and that combining conventional filtration with ozone treatment will meet future safe drinking water standards and provide additional assurance of safer, aesthetically pleasing drinking water.

Further work will determine costs for this portion of the water supply system before each City Council is asked to confirm the recommendation in December 2010.  Of the 18 alternatives examined, this treatment recommendation is considered mid-range in terms of cost.

To learn more about the water treatement decision, read:

* The 2007 Joint Water Supply System Analysis or "Carollo Report" is available in the Library.


Ozone is oxygen (O2) with an extra atom (O3).  Ozone treatment works through a process called “oxidation.”  During oxidation, the extra atom oxidizes, or destroys, odor-causing material and microorganisms, leaving only pure oxygen in the water.  A generator uses energy to produce ozone from oxygen for the water treatment process.  Lightning storms naturally produce ozone; that is what creates the clean, "after-rainstorm" smell.   

The use of ozone for water treatment has many benefits.  It:

  • Provides an additional treatment barrier to protect public health
  • Consistently produces water that is pleasant tasting, year round.
  • Reduces the amount of chlorine needed for disinfection.
  • Is capable of meeting emerging concerns for pathogens, algal toxins, disinfection by-products, pharmaceuticals and personal care products.
  • Represents proven technology, with the number of ozone installations increasing in Oregon and across the U.S. due to its ability to provide multiple water quality benefits.
  • Offers multiple benefits at cost to an average household of less than $0.20 per day.

Water Treatment Decision --2010 Meetings

Meeting Date/Location
Expert Panel Workshop #1
Summary Report. (PDF 236 kb)
March 25, 2010
Crowne Plaza Hotel
Expert Panel Workshop #2
Summary Report 2. (PDF 331 kb)
April 21, 2010
Crowne Plaza Hotel
Oversight Committee May 3, 2010
Crowne Plaza Hotel

Lake Oswego Council Study Session

June 8
Lake Oswego City Hall

Expert Panel #3 and Sounding Board
Summary Report 3 . (PDF 211 kb)

June 10
Crowne Plaza Hotel

Oversight Committee

June 14
Tigard Public Library
Tigard City Council/IWB Meeting

June 15
Town Hall, Tigard

Water Partnership Open House

June 24
West End Building
Joint Council Study Session

July 12
West End Building

Meeting Descriptions

Expert Panel A panel of national and regional experts in water treatment and public health was invited to provide insight into the best treatment options for the Lake Oswego Tigard Partnership.  The panelists’ evaluation factors include costs and benefits, economic, environmental and community risks and opportunities.  On June 10, the Expert Panel concluded their review by recommending a preferred treatment method.

Click here to learn more about the Expert Panel. (PDF 44 kb)

Citizen Sounding Board This group of Lake Oswego and Tigard citizens was organized to provide a customer’s perspective on the discussions of the expert panel to the two City Councils.  They met in the evening after the Expert Panel meetings. For more information, click here.

Oversight Committee The Oversight Committee is a four-person advisory group with members from the City of Tigard and City of Lake Oswego City Councils.  They discussed the treatment options and other project details at their meetings in May and June.

Lake Oswego City Council, the Tigard City Council and the Intergovernmental Water Board (IWB) The Intergovernmental Water Board and each City Council held separate study sessions in May and June to learn about treatment options.  

The process culminated with a joint meeting of both Tigard and Lake Oswego City Councils on July 12, 2010.