Water System Plan

Person Filling a Water Glass in a Sink


To ensure reliable and safe drinking water for decades to come, Issaquah is now planning for our future needs.

Currently, Issaquah’s water comes from two separate sources:

  • Groundwater: In general, residents in Squak Mountain, Olde Town and Issaquah Valley have always received water from a complex system of groundwater wells that pump from the Issaquah Aquifer.
  • Regional water: Starting in the late 1990s, Issaquah started to purchase regional water from Cascade Water Alliance to accommodate new growth. Today, Issaquah Highlands, as well as Lakemont, Montreux and South Cove, all receive regional water.

Meanwhile, the Talus community can receive either groundwater or regional water, depending on multiple factors (such as a hot weather season).

Water System Plan

Issaquah’s population is estimated to grow from 37,000 in 2017 to approximately 50,000 by 2027, with much of that growth focused in the Central Issaquah Area along I-90. 

Due to that projected growth, the City’s existing groundwater supply will not meet the demand in Issaquah Valley. 

In 2018, the City Council adopted a Water System Plan Update that recommends building a new treatment plant south of the Interstate 90 corridor in Issaquah Valley.

A centralized plant would: 

  • Enable the blending of groundwater and regional (fluoridated) water.
  • Address differing water qualities in each groundwater well.
  • Deliver consistent water quality between regional and groundwater.
  • Allow Issaquah to be more responsive to new/emerging water quality regulations.

Currently, about two-thirds of Issaquah residents receive fluoridated water, while one-third receive unfluoridated water. See Issaquah’s fluoridation map for further details.

Learn more about fluoride via Seattle Public Utilities, which started adding fluoride to its water in 1970 (a full history is also available online).

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