Rosemead, CA tap water
Supplied mostly by Gswc-South San Gabriel, plus 4 other utilities. Here's what the water means for your fish.
Disinfectant
Chlorine or chloramine
Utilities here use chlorine or chloramine, depending on which one serves your address. Chlorine slowly gases off from standing water; chloramine doesn't.
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 EPA monitoring data; California Water Board lab results (2014–2025).
Nitrate (NO₃)
5.3–32 ppm (Worth knowing)
Typical 15 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
0.06–0.17 ppm (Worth knowing)
Typical 0.13 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 (2023–2025).
Water chemistry
General hardness
Supplier's figure17–291 ppm
Typical 234 ppm
Hard. Ideal for livebearers and African cichlids. Soft-water species may struggle to breed.
From the utility that supplies yours: Metropolitan Water Dist. of So. Cal., which supplies Gswc-South San Gabriel; Metropolitan Water Dist. of So. Cal. and Sierra Madre-City, Water Dept., which supplies Cal/Am Water Company - San Marino; California Water Board lab results; California Water Board lab results, measured before treatment (2023–2026).
Carbonate hardness (alkalinity)
Supplier's figure68–220 ppm
Typical 128 ppm
Strong buffering. pH stays steady and hard to lower without RO water.
From the utility that supplies yours: Metropolitan Water Dist. of So. Cal., which supplies Gswc-South San Gabriel; Metropolitan Water Dist. of So. Cal. and Sierra Madre-City, Water Dept., which supplies Cal/Am Water Company - San Marino; California Water Board lab results; California Water Board lab results, measured before treatment (2023–2026).
pH
7–8.4
Typical 7.8
Most community fish do well here. Stable water matters more than the exact number.
From EPA monitoring data; California Water Board lab results; California Water Board lab results, measured before treatment (2014–2026).
Total dissolved solids
Supplier's figure160–666 ppm
Typical 480 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: Metropolitan Water Dist. of So. Cal., which supplies Gswc-South San Gabriel; Metropolitan Water Dist. of So. Cal. and Sierra Madre-City, Water Dept., which supplies Cal/Am Water Company - San Marino; California Water Board lab results; California Water Board lab results, measured before treatment (2023–2026).
Who supplies Rosemead, CA
Gswc-South San Gabriel
Serves 36% of residents · Buys water from Metropolitan Water Dist. of So. Cal. · Chloramine
Cal/Am Water Company - San Marino
Serves 32% of residents · Buys water from Metropolitan Water Dist. of So. Cal. · Chloramine
San Gabriel Valley Water Co.-El Monte
Serves 14% of residents · Groundwater (wells) · Chlorine
San Gabriel County WD
Serves 9% of residents · Groundwater (wells) · Chlorine
Amarillo Mutual Water Company
Serves 6% of residents · Groundwater (wells) · 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.