Water System Plan


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 (CWA) 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).

Planning for the Future

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 Interstate 90. Due to that projected growth, the City’s existing groundwater supply will not meet the demand in Issaquah Valley. 

To plan ahead, in 2018 the City Council adopted a Water System Plan Update that recommended building a new treatment plant south of the I-90 corridor in Issaquah Valley to enable expanded service.

The City Council, however, revised that plan in 2020 when CWA started offering its supply at a significantly lower cost, as long as any discounted regional water replaces some of Issaquah’s production from its groundwater wells.

Issaquah’s new strategy means it won’t need a centralized water treatment plant until at least 2030 or beyond — depending on growth and other factors.

While many Issaquah residents receive fluoridated water, some still receive unfluoridated water. See Issaquah’s fluoridation map for further details.

To provide consistency between the City’s remaining well water (which is currently not fluoridated) and the additional CWA water (which is fluoridated), the City plans to fluoridate its entire system by mid-2022. To help pay for these upgrades, the City recently acquired a grant from the Arcora Foundation.

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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