Washington City, specifically
210 to 656 ppm, and why your tankless heater cares.
Washington City’s 2025 water quality report gives total dissolved solids as 210 to 656 ppm, and sulfate as 32 to 198 ppm. That is a genuine range, not a single number, because the city draws from more than one place.
Now the other half. Rinnai and Rheem both cap total dissolved solids at 500 mg/L in their warranty and installation documents, alongside a 200 mg/L hardness cap. Those are the manufacturers’ own figures, published in their own paperwork.
656 is more than 500. So at the top of this city’s published range, the water is outside what the manufacturer warranted the appliance to run on. That does not mean your heater will fail tomorrow, and it does not mean a warranty claim gets denied automatically. It means the question is worth asking before you buy a tankless unit here, and it is worth knowing if one has just failed on you.
Nobody in this market will tell you that, because it costs a tankless sale. We would rather you bought the right appliance and stayed a customer. Ask us what your treatment options are, and ask us to show you the manufacturer’s own hardness and TDS page before you sign anything.
One more thing that is specific to this city and catches people out: the electric utility is split. Washington City Power serves north of the Virgin River and Dixie Power serves the rest of the city limits. Rocky Mountain Power serves no part of Washington City at all. When an electric water heater has no power, the side of the river you are on decides who you ring.
And the housing stock here is two different eras with two different pipe problems. Green Springs went up mainly through the 1990s and 2000s, which overlaps the tail of the polybutylene period — gray pipe, stamped PB2110, that fails from the inside. Long Valley Trails is current D.R. Horton new construction, where the failures are fittings and workmanship rather than material. Knowing which one you are standing in changes what we look at first.
