How hard is Johnson County water? What WaterOne's 2026 report means for your water heater and fixtures
By Prairie Village Plumbing Company · Published September 30, 2026 · Updated September 30, 2026
WaterOne's 2026 Water Quality Report puts average total hardness at 135 ppm, about 7.9 grains per gallon. Here's how to read that number and what it does to water heaters, faucets and fixtures.
If you live in Prairie Village, Mission Hills, Fairway, Leawood, Overland Park, Mission or Roeland Park, your water most likely comes from WaterOne, which lists all of those among the 17 cities it serves. WaterOne publishes an annual water quality report, and the hardness figure in it is the number you need for a water softener setting, a tankless heater’s maintenance schedule, or just understanding the white crust on your faucets.
The 2026 numbers
WaterOne’s 2026 Water Quality Report (which reports data for January 1 to December 31, 2025) lists:
- Total hardness: 135 ppm average, with a range of 110 to 157 ppm
- Calcium hardness: 79 ppm average, with a range of 64 to 120 ppm
“ppm” is parts per million, the same as milligrams per liter.
Converting to grains per gallon
Water softeners, dishwashers and many tankless water heaters ask for hardness in grains per gallon (gpg). WaterOne’s own FAQ gives the conversion: divide the most recent total hardness (ppm) by 17.1.
- Average: 135 ÷ 17.1 ≈ 7.9 gpg
- Range: 110 ÷ 17.1 ≈ 6.4 gpg to 157 ÷ 17.1 ≈ 9.2 gpg
If you’re programming a softener, use the current report’s average (and check it again each year, since the report updates).
Is that “hard”?
WaterOne already softens its water at the treatment plant. An older WaterOne report (the 2006 edition, covering 2005 data) explains that the utility uses lime (and sometimes soda ash) to reduce hardness, with a goal of keeping it between 120 and 140 mg/L, and says that even so, the water “is still classified as hard water.” The same report notes that further reducing hardness would add significant cost, and that there’s no evidence additional softening improves health or safety; some customers prefer it for aesthetic reasons. That report is 20 years old, but the 2026 average of 135 ppm falls inside the same 120–140 range.
So: moderately hard water, treated, safe, and hard enough to leave mineral deposits over time.
What hardness does in your home
Tank water heaters. As water is heated, dissolved minerals come out of solution and settle as sediment on the bottom of the tank. Over the years that layer can make a gas heater rumble or pop as it fires, slow recovery, and in electric heaters it can bury the lower element. Periodic flushing helps. See water heater repair.
Tankless water heaters. Scale builds up inside the heat exchanger, which restricts flow and triggers error codes. Manufacturers generally call for periodic descaling, and hard water makes it more important. See tankless water heaters.
Faucets and showerheads. Scale clogs aerators and showerhead nozzles and wears faucet and valve cartridges. Low flow at a single fixture is usually a scaled aerator, an easy fix.
Toilets. Mineral deposits can clog the rim jets that rinse the bowl and stiffen fill valves.
Glass and dishes. Spotting and film, which is mostly cosmetic.
Do you need a softener?
That’s a preference, not a requirement. At about 7.9 gpg, many households live without one and handle scale with routine maintenance: cleaning aerators, flushing the water heater, and descaling a tankless unit on schedule. Others prefer softened water for less spotting and scale. If you install one, set it using WaterOne’s current report.
A few practical notes if you’re considering one:
- A softener should be sized to your household’s use and the hardness number above.
- Many people leave a kitchen cold-water tap or an outdoor hose bibb unsoftened.
- Softener drain and installation details matter; a plumber should check the connection and drain point.
How to check your own provider
WaterOne lists its service cities on its website. A few areas of Johnson County are served by other utilities, and WaterOne itself lists De Soto and Olathe as only partially served. If you’re not sure, your water bill will say who your provider is, or call WaterOne at 913-895-1800.
Questions about what hardness is doing to your water heater or fixtures? Call us at (913) 305-5013.