SeaTac, WA tap water
Supplied mostly by Highline Water District, 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)
Supplier's figureUp to 12 ppm (Low)
Typical 0.2 ppm
Low, so water changes lower your tank's nitrate well.
From the utility that supplies yours: Seattle Public Utilities, which supplies Highline Water District; Seattle Public Utilities and Skyway Water & Sewer, which supplies King County Water District #125 (2012–2019).
Chlorine or chloramine at the tap
0.3–1.7 ppm
Typical 0.7 ppm
At tap levels, chlorine and chloramine are toxic to fish, shrimp and the bacteria in a filter. Water conditioners are made for this range.
Published by your utility: Highline Water District's 2025 water quality report.
Water chemistry
General hardness
Supplier's figure25 ppm
Soft. Good for tetras, rasboras and most shrimp. Livebearers, snails and African cichlids prefer harder water.
From the utility that supplies yours: Seattle Public Utilities, which supplies Highline Water District; Seattle Public Utilities, which supplies King County Water District #125.
Carbonate hardness (alkalinity)
Supplier's figure23 ppm
Little buffering. pH can drop quickly between water changes, especially with CO₂ or an older tank.
From the utility that supplies yours: Seattle Public Utilities, which supplies Highline Water District; Seattle Public Utilities, which supplies King County Water District #125.
pH
Supplier's figure7.5–8.5
Typical 8.3
Alkaline. Many utilities raise pH to protect pipes. Stability matters more than the exact number.
From the utility that supplies yours: Seattle Public Utilities, which supplies Highline Water District; Seattle Public Utilities, which supplies King County Water District #125.
Total dissolved solids
Supplier's figure36 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 the utility that supplies yours: Seattle Public Utilities, which supplies Highline Water District; Seattle Public Utilities, which supplies King County Water District #125.
Who supplies SeaTac, WA
- 2025 water quality report
Highline Water District
Serves 79% of residents · Buys water from Seattle Public Utilities · Chlorine
King County Water District #125
Serves 15% of residents · Buys water from Seattle Public Utilities · 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.
Tap water lookup covers US cities only for now. Want to know why it matters? Read our story on tap water.
Compiled by Shoal & Stem from public records. Free to cite with a link.