Madison, WI tap water
Supplied by Madison Water Utility. Here's what its water means for your fish.
Disinfectant
Chlorine
Your water is treated with chlorine. It slowly gases off from standing water, and any water conditioner removes it.
Safety for fish and shrimp
Nitrite (NO₂)
0.03 ppm (Low)
Essentially none, so any nitrite in your tank comes from the tank itself.
Published by your utility: Madison Water Utility's 2025 water quality report.
Nitrate (NO₃)
Up to 16 ppm (Low)
Typical 3.5 ppm
Low, so water changes lower your tank's nitrate well.
From EPA monitoring data (2012–2019).
Chlorine or chloramine at the tap
0.2–0.4 ppm
Typical 0.3 ppm
At tap levels, chlorine and chloramine are toxic to fish, shrimp and the bacteria in a filter. Water conditioners are made for this range.
Published by your utility: Madison Water Utility's 2025 water quality report.
Water chemistry
General hardness
308–343 ppm
Typical 325 ppm
Hard. Ideal for livebearers and African cichlids. Soft-water species may struggle to breed.
Published by your utility: Madison Water Utility's website.
Carbonate hardness (alkalinity)
270–342 ppm
Typical 318 ppm
Strong buffering. pH stays steady and hard to lower without RO water.
From EPA monitoring data (2017–2018).
pH
7.4–7.6
Typical 7.4
Most community fish do well here. Stable water matters more than the exact number.
From EPA monitoring data (2017–2018).
Total dissolved solids
Area estimate92–497 ppm
Typical 258 ppm
A rough measure of everything dissolved in the water. RO water reads near 0, so TDS is a quick way to compare waters.
Area estimate from nearby wells: USGS well samples in your state (2000–2023).
Who supplies Madison, WI
- 2025 water quality report
Madison Water Utility
Serves 95% 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.
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.