Utilities / Washington

Washington water hardness

2 Washington systems with a hardness figure read from an official page, each on the retrieval date printed against it below. This is not a list of every utility in Washington; it is the list of those whose published figure has been verified here.

Soft Soft 0–60

Moderately hard Moderate 61–120

Hard Hard 121–180

Very hard Very hard 181+

Seattle, WA 19.1 mg/L 1.1 gpg Soft
Spokane, WA 159 mg/L 9.3 gpg Hard

mg/L as calcium carbonate. Each classification band is drawn the same width, so the axis is not linear in mg/L.

Washington systems on the USGS classification. Each row links to that system's published figure, report year and conversion. Grains per gallon are the utility's own figure where it published one, and our conversion at 17.1 mg/L per grain where it did not.

Seattle, WA — Seattle Public Utilities 19.1 mg/L (1.1 gpg) Soft Published range 8.6–29.6 mg/L. Seattle Public Utilities Quarterly Surface Water Analysis, May 2026 (2nd Quarter 2026). Retrieved 2026-10-26.
Spokane, WA — City of Spokane Water Department 159 mg/L (9.3 gpg) Hard Published range 90.6–360 mg/L. City of Spokane Water Department 2025 Technical Drinking Water Report (Appendix III, Drinking Water Inorganics Summary). Retrieved 2026-10-26.

If your Washington system is not above

Only 2 Washington systems have been transcribed here, so most Washington readers will not find theirs. Find the water system that serves you walks through the free EPA search that names your system and the EPA lookup that finds its annual report, which is the document that carries a hardness figure for your water. There is no ZIP-code hardness figure on this site, and that page explains why a ZIP code cannot carry one honestly: a ZIP code is a postal boundary and a water system is a pipe network, and they do not line up.

Other states with verified systems

All verified systems Convert a figure from your own report How to read a water quality report