South San Francisco, CA tap water
Supplied mostly by California Water Service-S San Francisco, plus 1 other utility. Here's what the water means for your fish.
Disinfectant
Chloramine
Your water is treated with chloramine. Unlike chlorine, it doesn't gas off when water sits out, and many pitcher and fridge filters aren't rated to remove it. Conditioners that list chloramine on the label break it apart, which frees a little ammonia. Some utilities switch to plain chlorine for a few weeks a year.
Safety for fish and shrimp
Nitrite (NO₂)
Not detected (Low)
Not detected in testing, so any nitrite in your tank comes from the tank itself.
From California Water Board lab results (2024–2026).
Nitrate (NO₃)
Up to 5.3 ppm (Low)
Typical 5.3 ppm
Water changes can't take your tank's nitrate below this level.
From California Water Board lab results; San Francisco Regional Water System, which supplies Westborough Water District (2023–2026).
Copper at home taps
0.04–0.06 ppm (Low)
Typical 0.04 ppm
Low. Water that sits in household pipes overnight can carry more than this.
From California Water Board lab results (2025).
Water chemistry
General hardness
Estimate8–380 ppm
Typical 380 ppm
Hard. Ideal for livebearers and African cichlids. Soft-water species may struggle to breed.
Estimated from California Water Service-S San Francisco's calcium and magnesium readings; San Francisco Regional Water System, which supplies Westborough Water District (2023–2026).
Carbonate hardness (alkalinity)
Supplier's figure8–102 ppm
Typical 84 ppm
Moderate buffering. pH should stay fairly steady.
From the utility that supplies yours: San Francisco Regional Water System, which supplies California Water Service-S San Francisco; San Francisco Regional Water System, which supplies Westborough Water District (2023–2025).
pH
7.2–9
Typical 7.2
Most community fish do well here. Stable water matters more than the exact number.
From California Water Board lab results; San Francisco Regional Water System, which supplies Westborough Water District (2023–2026).
Total dissolved solids
Supplier's figure24–269 ppm
Typical 146 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: San Francisco Regional Water System, which supplies California Water Service-S San Francisco; San Francisco Regional Water System, which supplies Westborough Water District (2023–2025).
Who supplies South San Francisco, CA
California Water Service-S San Francisco
Serves 82% of residents · Buys water from San Francisco Regional Water System · Chloramine
Westborough Water District
Serves 21% of residents · Buys water from San Francisco Regional Water System · Chloramine
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.