Lehi’s 2025 water quality report doesn’t list a hardness figure, so there’s no official number to plan a flush schedule around. What it does list is total dissolved solids of 120–388 mg/L, from a supply made up of Lehi City wells and springs plus Central Utah Water Conservancy District surface water. Until you test your own water, the sensible default is the one Navien gives: descale at least once a year, and sooner if the heater starts showing scale or service codes.
Flush My Tankless started here in 2021 as a hands-on tankless flushing service, and it now connects Lehi homeowners with independent technicians who do the work.
Lehi water and your tankless heater
Lehi City lists its sources as seven wells and three springs, plus surface water bought from the Central Utah Water Conservancy District (CUWCD). That makes Lehi a blended system. A deep well, a spring and a treatment plant can each deliver water with a different mineral load.
The dissolved-solids range hints at that spread. Total dissolved solids (TDS) is everything left behind when the water evaporates: the calcium and magnesium that form scale, but also sodium, sulfate and other minerals that don’t. So TDS is not hardness, and it can’t tell you how quickly scale will build inside a heat exchanger (the coiled metal passage where the burner heats your water). A range as wide as Lehi’s does tell you the sources aren’t alike.
What the district’s numbers can and can’t tell you
CUWCD publishes hardness for its own water, and it’s tempting to borrow it. Its 2021 report gives an average of 8.2 gpg for treated water leaving its Don A. Christiansen plant, and 4.3 gpg for groundwater from its Central Water Project wells, which run about 1,500 feet deep.
Those figures describe the district’s wholesale water. They don’t describe what comes out of a faucet in Lehi, because the city mixes district water with its own wells and springs, and those have no published hardness. Use the district numbers as background, not as your answer.
Getting a real number for your house
Two cheap steps settle the question:
- Ask Lehi City. The water department can tell you which sources usually feed your part of town and whether it has hardness results it hasn’t published.
- Test at the tap. A hardness test strip from a hardware or pool store reads in gpg (grains per gallon) or mg/L. Test cold water from a kitchen faucet, not water that has passed through a softener.
Then hold your result up against the limit in your heater’s manual. Brands draw the line in different places:
| Your tap test | Over the published limit for |
|---|---|
| Above 100 ppm | Bosch |
| Above 7 gpg | Bosch, Takagi and A.O. Smith (7 gpg) |
| Above 200 ppm | The above, plus Rinnai and Rheem (200 ppm) |
| Above 12 gpg | All of the above, plus Navien and Noritz (12 gpg) |
Over your brand’s line, the manuals call for a water softener or a scale-prevention device, and scale damage is generally left out of the warranty.
What a blended supply means in Lehi homes
No published source breaks down Lehi’s housing or where its tankless heaters tend to be installed, so this page won’t guess. The water data does point to a few practical things.
A neighbor’s test result may not match yours, since different parts of a blended system can lean on different sources. Lehi’s report lists its sources but not which neighborhoods each one serves, so the water department is the place to ask. The heater itself is a useful gauge, too. Many units have a flush reminder an installer can set: Rinnai’s SENSEI models offer every 6 months, 1 year or 2 years (installer-selected), and Navien’s NPE-2 offers no alarm, 6, 12 or 24 months. Once you know your hardness, set the reminder to match rather than leaving it off.
Finally, keep notes. If a technician flushes the unit and very little scale comes out after a year, yearly is probably enough for your address. If the descaling solution comes back cloudy and gritty, shorten the gap.
Services for Lehi homeowners
- Tankless flush and descale: the core job, and a good way to learn how fast scale builds on your particular mix of Lehi water.
- Yearly maintenance visit: the flush plus an inlet filter cleaning and a look at venting, condensate and error history.
- Repair and error codes: for a unit that has already thrown a scale or overheat code, or lost hot water.
- Replacement or new install: ask for isolation valves if the old unit didn’t have them, since every later flush depends on them.
- Softeners and scale prevention: worth pricing once your test strip reads over your brand’s limit.
On price, HomeGuide’s 2026 guide puts a professional tankless flush at $150–$350; the technician serving Lehi confirms your price when you book.