Lake San Marcos, CA tap water
Supplied by Vallecitos WD. Here's what its 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
Nitrate (NO₃)
Supplier's figureUp to 1 ppm (Low)
Typical 0.5 ppm
Low, so water changes lower your tank's nitrate well.
From the utility that supplies yours: San Diego County Water Authority and Olivenhain MWD, which supplies Vallecitos WD (2023–2026).
Copper at home taps
0.07 ppm (Low)
Low. Water that sits in household pipes overnight can carry more than this.
From California Water Board lab results (2024).
Water chemistry
General hardness
Supplier's figure209–228 ppm
Typical 218 ppm
Hard. Ideal for livebearers and African cichlids. Soft-water species may struggle to breed.
From the utility that supplies yours: San Diego County Water Authority and Olivenhain MWD, which supplies Vallecitos WD (2024–2026).
Carbonate hardness (alkalinity)
Supplier's figure105–119 ppm
Typical 112 ppm
Strong buffering. pH stays steady and hard to lower without RO water.
From the utility that supplies yours: San Diego County Water Authority and Olivenhain MWD, which supplies Vallecitos WD (2023–2026).
pH
Supplier's figure7.9–8.2
Typical 8
Alkaline. Many utilities raise pH to protect pipes. Stability matters more than the exact number.
From the utility that supplies yours: San Diego County Water Authority and Olivenhain MWD, which supplies Vallecitos WD (2023–2026).
Total dissolved solids
Supplier's figure500–520 ppm
Typical 510 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 Diego County Water Authority and Olivenhain MWD, which supplies Vallecitos WD (2023–2026).
Who supplies Lake San Marcos, CA
Vallecitos WD
Serves all residents · Buys water from San Diego County Water Authority · 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.