Eureka, CA tap water
Supplied mostly by Humboldt Bay MWD, plus 1 other utility. Here's what the water means for your fish.
Disinfectant
Chlorine
Your water is treated with chlorine. It slowly gases off from standing water, and any water conditioner removes it.
Safety for fish and shrimp
Nitrate (NO₃)
Not detected (Low)
Not detected in testing, so water changes lower your tank's nitrate well.
From California Water Board lab results, measured before treatment; Humboldt Bay MWD, which supplies City of Eureka, measured before treatment (2023–2024).
Copper at home taps
0.55–0.81 ppm (High)
Typical 0.81 ppm
Shrimp and snails are sensitive to copper. Water that sits in household pipes picks up the most; it drops once the tap has run for a minute.
From California Water Board lab results (2023–2024).
Water chemistry
General hardness
77 ppm
Moderately soft to medium. Suits most community fish and plants.
From California Water Board lab results, measured before treatment; Humboldt Bay MWD, which supplies City of Eureka, measured before treatment (2025).
Carbonate hardness (alkalinity)
70 ppm
Moderate buffering. pH should stay fairly steady.
From California Water Board lab results, measured before treatment; Humboldt Bay MWD, which supplies City of Eureka, measured before treatment (2025).
pH
7.1–7.4
Typical 7.1
Most community fish do well here. Stable water matters more than the exact number.
From California Water Board lab results, measured before treatment; EPA monitoring data (2012–2025).
Total dissolved solids
100 ppm
A rough measure of everything dissolved in the water. RO water reads near 0, so TDS is a quick way to compare waters.
From California Water Board lab results, measured before treatment; Humboldt Bay MWD, which supplies City of Eureka, measured before treatment (2025).
Who supplies Eureka, CA
Humboldt Bay MWD
Serves 51% of residents · Groundwater (wells) · Chlorine
City of Eureka
Serves 51% of residents · Buys water from Humboldt Bay MWD · Chlorine
Our data comes from public records and is still incomplete. Many utilities don't publish every number, so we're adding more all the time. Your city's range is a starting point: testing your own tap is the only way to know exactly what's in it.
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Compiled by Shoal & Stem from public records. Free to cite with a link.