Your water heater has started making noise. A low rumble, or a series of pops, usually right after someone takes a shower. The unit still works, so it is easy to ignore.
That sound is not the tank failing. It is minerals boiling under a layer of sediment at the bottom of it.
Most homes in Sunnyvale and the surrounding cities have hard water. Hardness here runs somewhere between seven and nineteen grains per gallon depending on the neighborhood and the source your utility is drawing from. On the low end, that is simply “hard.” On the high end, it is about as hard as residential water gets in California.
Here is what that actually does to the equipment and what is worth doing about it.
What a grain per gallon really measures
Hardness is just the amount of dissolved calcium and magnesium in your water. It gets measured in grains per gallon, shortened to GPG.
Anything above roughly seven GPG is considered hard. Above ten, plumbers start seeing the effects on water heaters and fixtures within a few seasons. Above fifteen, scale becomes the main reason equipment fails early.
You cannot see these minerals in a glass of water. You see them everywhere else. The white crust on the shower head. The film on glass doors that never fully wipes off. Soap that will not lather. A kettle with a chalky ring inside.
Every one of those deposits is also forming inside your water heater.
Why hardness varies so much across the county
Water in Santa Clara County comes from more than one place. Some of it is local groundwater pumped from wells. Some is treated surface water. Some is imported from outside the region.
Groundwater picks up minerals as it moves through soil and rock, so it tends to be significantly harder. Imported surface water is usually much softer. Utilities blend these sources, and the blend shifts by service zone and by season.
That is why one Sunnyvale homeowner deals with constant scale and a neighbor two miles away barely notices it. Your water district publishes a hardness figure for your zone, and it is worth looking up before you spend money on treatment.
What happens inside a tank water heater
Heat is what pulls minerals out of solution. When hard water is heated, calcium separates and settles.
In a standard tank unit, that sediment collects on the bottom, directly above the burner. Over time it forms a hard crust that behaves like insulation. The burner now has to fire longer and hotter to push heat through that layer and into the water.
Three things follow:
The unit uses more gas to deliver the same hot shower. Water trapped underneath the sediment layer flashes to steam and escapes through it, which is the popping and rumbling you hear. And the steel at the bottom of the tank runs hotter than it was designed to, which shortens the life of the glass lining and the tank itself.
A water heater that should last a decade or more can start leaking years early in hard water. The failure looks sudden. It was not.
Scale also coats the anode rod, the sacrificial metal rod that protects the tank from corrosion. Once it is buried in mineral deposits, it stops doing its job quietly, and the tank starts corroding from the inside.
Tankless units feel it faster
Tankless heaters are more efficient and take up almost no space, which is why so many homeowners here switch to them. They are also less forgiving about hard water.
A tankless unit heats water instantly by pushing it through a narrow heat exchanger. There is no tank for sediment to fall into. The minerals deposit directly on the walls of the exchanger and inside the passages the water travels through.
Those passages are small to begin with. A thin layer of scale restricts flow, drops the output temperature, and makes the burner work harder. Left alone long enough, it triggers error codes and eventually damages the exchanger, which is the single most expensive part of the unit.
This is why almost every manufacturer requires descaling as a condition of the warranty and why the recommended interval gets shorter as hardness goes up. In a home at fifteen GPG, an annual descale is a minimum, not a suggestion. We cover that process on our tankless water heater maintenance page.
Signs your heater is already scaled up
You do not need a technician to notice the early ones.
Hot water runs out faster than it used to because sediment is occupying volume the tank used to hold. The unit rumbles, pops, or crackles during and after heating. Your gas bill creeps up without any change in how much hot water your household uses.
At a fixture, you may see reduced hot water pressure while cold pressure is normal or flakes of white and brown material in the aerator screens. On a tankless system, the temperature swings mid-shower or the unit throws a flow-related fault.
Rust-colored water from the hot side only is a later sign, and it usually means the anode rod is spent and the tank is corroding.
Flushing is the cheapest thing you can do
Draining and flushing a tank heater clears the loose sediment before it hardens into a crust. It is straightforward maintenance, and in hard water it matters more than anywhere else.
Once a year is the standard recommendation. In a home at the higher end of the hardness range, twice a year is a better fit, and it costs far less than the efficiency you lose by skipping it.
There is one honest caveat. A flush removes loose sediment. It does not remove scale that has already bonded to the tank floor or to a heat exchanger. That is why the timing matters. A heater flushed regularly from the start stays clean. A heater flushed for the first time after many years of neglect often just confirms how much damage is already there.
If yours has never been serviced, water heater maintenance is the place to start, along with an anode rod check while the unit is drained.
Softener, scale inhibitor, or nothing at all
Flushing manages the symptom. Treating the water addresses the cause.
A traditional softener uses ion exchange to swap calcium and magnesium for sodium. It is the most effective option and the one that protects everything downstream, including your fixtures, your dishwasher, and your washing machine. It needs salt, a drain connection, and periodic attention. A few California districts have rules about brine discharge, so it is worth confirming what applies where you live before you buy one.
A scale inhibitor, sometimes sold as a salt-free conditioner, does not remove minerals. It changes their structure so they are less likely to stick to surfaces. It requires no salt and no drain, and it is a reasonable middle option for a household mainly trying to protect a tankless unit.
Reverse osmosis is a separate question. It treats drinking water at one faucet and does nothing for the water heater. Homes here often end up with both: a whole-house softener or conditioner for the plumbing and a small RO system under the kitchen sink for taste.
Which of these makes sense depends on your actual hardness number, your household size, and whether you are protecting a tank or a tankless unit. Our water softener and filtration page walks through the differences in more detail.
The practical version
If your water heater is newer, flush it on schedule and check the anode rod. That alone buys you years.
If it is older and has never been flushed, have it inspected before you decide. Sometimes the right call is maintenance. Sometimes the tank is far enough gone that replacement is the better use of the money, and knowing that before it leaks is worth a lot.
If you are running a tankless unit anywhere in Santa Clara County, put descaling on the calendar and keep it there. It is the difference between a long service life and a heat exchanger replacement.
JetPipe Plumbing works on tank, tankless, hybrid, and heat pump water heaters across Sunnyvale and the South Bay, and we handle softener and filtration installs on the same visit when it makes sense. Same-day service is available, and estimates are free.