O'Fallon, MO tap water
Supplied mostly by St Charles County Pwsd 2, 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 EPA monitoring data (2012–2019).
Nitrate (NO₃)
Supplier's figure1.8–6.3 ppm (Low)
Typical 6 ppm
Water changes can't take your tank's nitrate below this level.
From the utility that supplies yours: St Louis City PWS, which supplies St Charles County Pwsd 2; Missouri American Water – St. Louis St. Charles Counties, which supplies Ofallon PWS; EPA monitoring data (2012–2019).
Copper at home taps (first draw)
Up to 0.06 ppm (Low)
The 90th percentile of first-draw samples from homes: water that sat in household pipes for at least six hours.
Low. Water that sits in household pipes overnight can carry more than this.
Published by your utility: Missouri American Water – St. Louis St. Charles Counties' 2025 water quality report.
Water chemistry
General hardness
67–223 ppm
Typical 163 ppm
Moderately hard. Great for livebearers, and most community fish adapt.
From St Charles County Pwsd 2's 2025 water quality report; St Charles County Pwsd 2 and Missouri American Water – St. Louis St. Charles Counties, which supplies Ofallon PWS; Missouri American Water – St. Louis St. Charles Counties' website.
Carbonate hardness (alkalinity)
83–200 ppm
Typical 104 ppm
Moderate buffering. pH should stay fairly steady.
From St Charles County Pwsd 2's 2025 water quality report; St Charles County Pwsd 2 and Missouri American Water – St. Louis St. Charles Counties, which supplies Ofallon PWS; Missouri American Water – St. Louis St. Charles Counties' 2025 water quality report.
pH
7.6–10.2
Typical 8.7
Alkaline. Many utilities raise pH to protect pipes. Stability matters more than the exact number.
From St Charles County Pwsd 2's 2025 water quality report; EPA monitoring data; Missouri American Water – St. Louis St. Charles Counties' website (2014–2025).
Total dissolved solids
333–410 ppm
Typical 372 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 St Charles County Pwsd 2's 2025 water quality report; St Charles County Pwsd 2, which supplies Ofallon PWS.
- Ofallon PWS and Missouri American Water – St. Louis St. Charles Counties add phosphate to protect pipes. It can feed algae in tanks without much plant growth.
- St Charles County Pwsd 2, Ofallon PWS and Missouri American Water – St. Louis St. Charles Counties soften their water at the plant, so it may be softer than the local groundwater.
Who supplies O'Fallon, MO
- 2025 water quality report
St Charles County Pwsd 2
Serves 64% of residents · Buys water from St Louis City PWS · Chloramine
Ofallon PWS
Serves 24% of residents · Buys water from St Charles County Pwsd 2 · Chloramine
- 2025 water quality report
Missouri American Water – St. Louis St. Charles Counties
Serves 8% 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.
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Compiled by Shoal & Stem from public records. Free to cite with a link.