San Dimas, CA tap water
Supplied mostly by Gswc-San Dimas, plus 2 other utilities. 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 (2023–2026).
Nitrate (NO₃)
Up to 15 ppm (Worth knowing)
Typical 11 ppm
Water changes can't take your tank's nitrate below this level.
From California Water Board lab results (2023–2026).
Copper at home taps
Up to 0.02 ppm (Low)
Typical 0.02 ppm
Low. Water that sits in household pipes overnight can carry more than this.
From California Water Board lab results (2023–2026).
Water chemistry
General hardness
Supplier's figure82–291 ppm
Typical 120 ppm
Moderately soft to medium. Suits most community fish and plants.
From the utility that supplies yours: Covina Valley Water Company - Wholesale and Three Valleys MWD and Walnut Valley Water District, which supplies Gswc-San Dimas; California Water Board lab results (2023–2026).
Carbonate hardness (alkalinity)
Supplier's figure68–220 ppm
Typical 110 ppm
Strong buffering. pH stays steady and hard to lower without RO water.
From the utility that supplies yours: Covina Valley Water Company - Wholesale and Three Valleys MWD and Walnut Valley Water District, which supplies Gswc-San Dimas; California Water Board lab results (2023–2026).
pH
7.2–8.7
Typical 7.2
Most community fish do well here. Stable water matters more than the exact number.
From EPA monitoring data; California Water Board lab results (2013–2026).
Total dissolved solids
Supplier's figure160–666 ppm
Typical 250 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: Covina Valley Water Company - Wholesale and Three Valleys MWD and Walnut Valley Water District, which supplies Gswc-San Dimas; California Water Board lab results (2023–2026).
Who supplies San Dimas, CA
Gswc-San Dimas
Serves 99% of residents · Buys water from Covina Valley Water Company - Wholesale · Chloramine
Three Valleys MWD
Serves 42% of residents · Lake or river water · Chloramine
Metropolitan Water Dist. of So. Cal.
Serves 17% of residents · Lake or river water · 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.
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.