Seattle Public Utilities Mami Hara, General Manager/CEO

Long-Range Water Demand Forecast and Firm Yield Estimate

Seattle Public Utilities (SPU) updates its official water supply yield estimate and long-range water demand forecast when it updates its Water System Plan or when significant new information becomes available.

The official forecast (pdf) was revised in July 2013 to reflect the newly-amended water supply declining block contract (pdf) with Cascade Water Alliance. Highlights from the official forecast include:

  • Water Supply: The yield estimate—172 million gallons per day (mgd)—remains the same as described in the 2013 Water System Plan.
  • Water Demand: Total demand is forecast to increase gradually to 142 mgd by 2039 and then decline to stay relatively flat at about 137 mgd through 2060.
  • Supply/Demand Implications: A new source of supply will not be needed until well after 2060. Taking demand uncertainty into consideration, there’s still more than a 90% probability that a new source will not be necessary before 2060.

Contact information

Joan Kersnar
Drinking Water Planning Manager
(206) 684-0839

Bruce Flory
Principal Economist
(206) 684-5859