Provo’s 2025 Water Report says the city’s water typically runs 10–15 gpg of hardness. That’s enough to scale a tankless heater steadily, and at the top of the range it’s over even the most lenient brand limits. If your Provo heater has no softener in front of it, a professional flush every year is the baseline, and sooner if the heater’s service reminder comes on.
Moderately hard, or very hard?
Provo describes its water as moderately hard. That label doesn’t match the U.S. Geological Survey’s scale. The USGS calls water hard at about 7.1–10.5 gpg and very hard at more than 10.5 gpg. Provo’s range starts in “hard” and ends well into “very hard.”
The label matters less than the comparison with your heater’s manual:
- At the low end, Provo is already past Takagi’s 7 gpg and Bosch’s 100 ppm.
- In the middle, it reaches Navien’s and Noritz’s 12 gpg.
- At the top, it’s over every major brand’s limit, including Rinnai’s 200 ppm.
Rinnai’s SENSEI manual lets the installer set the flush reminder to every 6 months, 1 year or 2 years (installer-selected) based on water conditions. On Provo water, the shorter settings are the realistic ones.
Limestone springs and valley wells
Provo City runs its own water system. It draws on Provo City springs and deep wells, and the 2025 Water Report explains where that water comes from underground: springs in limestone and quartzite plus wells in sand and gravel.
The geology helps explain the hardness. Limestone is mostly calcium carbonate, the same compound that makes up the white crust inside a scaled heat exchanger. Groundwater that travels through limestone dissolves some of it along the way and carries it to your tap. When the water is heated, that calcium comes back out of solution, and in a tankless heater it settles on the hottest surfaces first.
That’s also why scale builds faster at higher temperature settings. Rinnai says scale build-up is accelerated by high temperature settings, so setting the heater no hotter than you need is a cheap way to slow it down.
Doing it yourself on hard water
Flushing a tankless yourself is possible. The manufacturer procedures are straightforward on paper: close the isolation valves (the shutoffs on the hot and cold lines at the heater), then pump a descaler or white vinegar through the heat exchanger. Navien’s user’s manual calls for at least 45 minutes of circulation, and Rinnai’s SENSEI manual calls for 60 minutes.
Two catches matter on water this hard. Noritz says isolation valves are necessary, and not every install has them. And Navien warns that incorrect descaling could void the warranty if it damages the heater. If your unit has no valves, or is still under warranty, hiring the job out is the safer call. Our DIY vs professional guide walks through the trade-offs.
A new treatment plant on the way
Provo’s water picture is about to change. The city is building the Rock Canyon Water Treatment Plant, which will be able to treat 30 million gallons per day of Provo River water. Today Provo relies mainly on springs and wells. Once the plant is running, treated river water joins the mix.
We can’t say how that will affect hardness at any given tap, because the city hasn’t published that yet. River water and limestone-spring water aren’t the same, though, so it’s worth reading Provo’s water report when the plant comes online and re-testing your tap. If the number drops, your flush interval might stretch. If it doesn’t, nothing changes.
Springville
Springville, just south of Provo, runs its own water system. The Springville City Water System supplies groundwater from Springville City Water System springs and wells, and its 2025 Water Quality Report lists four springs and seven wells.
The city’s 2023, 2024 and 2025 reports don’t publish a hardness figure. The 2025 report does list total dissolved solids of 240–476 mg/L. TDS is the total of everything dissolved in the water, scale-forming calcium and magnesium included, so it can’t stand in for hardness. It does show that Springville’s sources vary.
Springville’s water comes entirely from its own springs and wells, so there’s no district surface water in the blend. For Springville tankless owners, a hardness test strip at a cold kitchen tap is the quickest way to find out whether your water is over your heater’s limit. Requests from Springville go through this page.
Services for Provo homes
- Scale removal: a tankless flush and descale clears the limestone-derived calcium described above.
- One yearly visit: annual maintenance bundles the flush with filter cleaning and a broader check.
- Error codes or no hot water: start with tankless repair.
- New or replacement units: installation covers swaps, conversions and the ThermWise rebate.
- Treating the water itself: scale prevention makes most sense at the top of Provo’s range.
Angi’s 2026 figures give $150–$250 for a tankless flush; your technician sets the price.