Eureka Water Hardness & Quality Report (2026)

Eureka, California, the Humboldt County seat — a major northwest California coastal city (Eureka is the Humboldt County seat — the largest city on the north California coast between San Francisco and Portland; Eureka is known for its extraordinary Victorian-era architecture (Eureka has one of the finest collections of Victorian residential and commercial architecture in the western United States — the Carson Mansion (built 1884–1886 by lumber baron William Carson) is one of the most photographed Victorian houses in America and is considered one of the finest examples of Queen Anne style Victorian architecture in existence); Eureka was the heart of the 19th century Humboldt Bay lumber industry (the redwood forests of Humboldt County were among the most productive lumber producing regions in California during the 19th and early 20th centuries)), home of Humboldt State University (now Cal Poly Humboldt — recently elevated to polytechnic status), a diverse Humboldt County community with a significant Native American, Latino-American, and working-class coastal population — draws its municipal water supply via the Humboldt Bay Municipal Water District. Water hardness in Eureka measures 81.5 mg/L — classified as moderately soft.

Eureka's moderate softness reflects the northwest California Humboldt County Franciscan watershed's calcareous-poor character. The Mad River and Jacoby Creek at Eureka–Humboldt County drain the Franciscan Complex greywacke (calcareous-poor). HBMWD produces the moderately soft 81.5 mg/L.

With hardness at 81.5 mg/L, Eureka residents enjoy moderately soft water. Humboldt Bay Municipal Water District consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.