Water Heaters in Hard-Water Country

Chapter overview

What does hard water do to a heater?

Heating hard water pulls calcium out of solution, and it settles in the tank as scale and sediment. The USGS notes that this scale can shorten equipment life and lowers the efficiency of electric water heaters (USGS). Rheem's manual for its high-efficiency gas tanks adds that deposits build faster at higher temperatures (Rheem AP21831).

Almost every tap in the area is well above Rheem's 0-5 grain line. The table uses each district's 2025 data; grains are hardness divided by 17.1, the conversion FPUD and Rainbow print. For a closer look at the numbers by neighborhood, see how hard North County water is §2.1.

The practical upshot is sediment management. The scale and flushing page §6.1 compares what each maker tells owners and why the interval printed in your own manual wins. A. O. Smith's gas manual goes further: it recommends water softening or threshold-type treatment where water is hard (A. O. Smith 324257).

What setting is safe?

About 120°F is the number every source here agrees on. The DOE's Energy Saver Guide calls 120°F a temperature considered safe for most people (DOE). SDG&E asks for 120°F or less to reduce scalding, and notes that a dishwasher without a booster heater may need 140°F (SDG&E appliance safety).

A. O. Smith ships its thermostat at the lowest setting and marks roughly 120°F as the preferred starting point. Higher settings raise scald risk and, per Rheem, speed up scale. The temperature and relief valve page §6.2 covers the dial, the scald cautions and what each manual says about the T&P lever.

What does California require?

State law requires bracing, anchoring or strapping on residential water heaters, whether new, replacement or existing, under Health & Safety Code 19211 (California Legislature). The 2025 California Plumbing Code §507.2 puts the straps in the upper third and lower third of the heater, with the lower strap at least 4 inches above the controls (IAPMO 2025 CPC). SDG&E adds that restraints belong on wall studs.

Garage gas heaters have one more rule: SDG&E says the pilot or other ignition source must sit at least 18 inches above the floor, though flammable-vapor-resistant (FVIR) units may be exempt. Homes with a pressure regulator or check valve also need thermal expansion control; see expansion tanks §3.3. The earthquake straps page §6.3 walks through placement and the seller's certification.

When is it time to replace?

None of the sources read for these pages gives a lifespan in years, so none is offered here. What they do show is that hard water shortens equipment life, and that replacement is licensed work: the gas hookup, the vent, the burner and the relief valve all belong to a licensed plumber.

Paperwork depends on where you live. Fallbrook, Bonsall, Rainbow and Valley Center sit in unincorporated County territory, where the County's PDS 110 form (revised January 2026) exempts a like-for-like replacement done by a licensed plumbing contractor. Escondido requires a permit for any water heater replacement, and Vista is a city with its own building department, so check with the city. Details and quote checks are on the replacement and permits page §6.4.

Any gas odor or hissing by the heater means everyone leaves the house first. Don't switch lights or appliances on or off, light anything or use anything that could spark inside; call SDG&E's gas emergency line or 911 once you are outside (SDG&E gas leaks). If you're unsure, call a licensed plumber.

Common questions

Q. Is a water heater in Fallbrook harder on parts than one on softer water?

By the sources here, yes in direction if not in years. FPUD's 13.7 grains sits well past the point where Rheem expects scale, and USGS links heated hard water to shorter equipment life. No source puts a number of years on the difference.

Q. Does Valley Center water vary enough to change heater care?

It can. VCMWD lists hardness per source and prints no blended figure: 230 mg/L in its Skinner water, 60.5 mg/L in the Carlsbad desal supply, or about 13.5 and 3.5 grains as we convert them. Plan maintenance for the harder number unless you know which source reaches your street.

Q. Who handles a heater problem that involves gas?

A licensed plumber or a technician qualified in gas appliance repair, which is how Rheem's manual puts it for relief-valve and venting inspection. A smell of gas is different: leave the building first, then call SDG&E or 911 from outside.

Q. Do the strapping rules differ between Escondido, Vista and the County?

No. Health & Safety Code 19211 is state law and covers residential heaters everywhere in California. What differs is the replacement permit: exempt for like-for-like swaps in the unincorporated County, required in Escondido, and a question for the City of Vista.

Q. Does a pressure regulator change anything for the water heater?

Yes. A regulator stops expanding hot water from flowing back to the main, so the 2025 California Plumbing Code §608.2 adds an expansion tank downstream of it. Rheem's manual links an occasionally discharging relief valve to that kind of closed system, and A. O. Smith says a properly sized expansion tank belongs on all closed systems.

Q. Why are so many garage water heaters raised off the floor?

Because of an SDG&E rule for garages: the flame that lights a gas heater has to be 18 inches or more off the floor. Heaters built to resist flammable vapors, sold as FVIR units, may not need the lift; the label on the tank tells you which kind you own.

Sources