Keeping a water heater from leaking, and what your town's water has to do with it

A tank water heater rusts from the inside, and nothing on the outside shows it until water is on the floor. Four small jobs slow that down. How often they need doing depends partly on what your town sends through the pipe.

Updated October 2026

The rod that rusts so the tank does not

Inside the tank hangs a metal rod called the anode. A. O. Smith's manual calls it a sacrificial rod that helps reduce corrosion and premature failure of the tank. The water eats the rod and leaves the steel alone.

A. O. Smith says rust-colored water from the hot taps suggests the rod has been used up.

The makers do not agree on how often to look at it. A. O. Smith says after the first six months and every year after that. Bradford White says every two years. Rheem's manual says to replace it when more than six inches of the core wire is showing.

The rod unscrews from the top of the tank and lifts straight out, so it needs room overhead. Most people have a plumber check it during the yearly flush.

A heater should never run without one. Bradford White says taking the anode out voids the warranty and shortens the life of the tank.

Sediment

Minerals in the water settle to the bottom of the tank as it heats. Rheem and A. O. Smith both say a rumbling or popping noise while the heater runs is usually that sediment.

How often to clear it depends on whose manual you read.

The job is a garden hose on the drain valve at the bottom of the tank, run to a floor drain or outside, with the cold supply closed. On an electric heater, turn the breaker off first. The water coming out is hot. Your heater's manual has the steps for your model.

A drain valve that has not been opened in ten years does not always close tightly again. On an old tank, have a plumber do the first one.

The relief valve

Near the top of the tank is a valve with a small lever and a pipe running down toward the floor. It opens if the temperature or the pressure inside gets too high.

A. O. Smith, Rheem and Bradford White all say to work it by hand at least once a year. Put a bucket under the pipe, lift the lever, let some water run, and let it snap shut.

If it will not close again, call a plumber. If it drips on its own between tests, A. O. Smith says that usually means the pressure in the house is too high or the system needs an expansion tank. Never cap the pipe.

Pressure

The Massachusetts plumbing code requires a pressure reducing valve wherever the pressure is over 80 pounds per square inch. A. O. Smith recommends running a heater at no more than 50 to 60. A gauge that screws onto an outside faucet reads it.

There is a second pressure problem that a gauge will not show while the water is cold. Water expands when it is heated. If the meter has a check valve or a backflow preventer on it, the extra volume cannot push back into the street. An A. O. Smith bulletin puts a number on it: water in a closed tank at 50 psi, heated 10 degrees, reaches 250 psi.

The same code section requires an expansion tank on a closed system. It is the small tank on the cold line above the heater. They wear out. Amtrol's tanks have an indicator cap, and Amtrol says a discolored cap means the tank has to be replaced.

Temperature

The Department of Energy says most households need only 120 degrees, and that 120 also slows mineral buildup and corrosion in the heater and the pipes. A. O. Smith ships its heaters set to about 120.

What your town sends you

Hard water carries more minerals and leaves more sediment in a tank. The U.S. Geological Survey measures hardness in milligrams per liter and sorts it this way: up to 60 is soft, 61 to 120 is moderately hard, 121 to 180 is hard, and over 180 is very hard.

MWRA water is soft. MWRA puts its hardness at about 16 milligrams per liter, which is one grain per gallon. In Quincy and Milton scale is a small problem and a yearly flush is plenty.

The annual water reports for the other towns do not print a hardness number. Sharon's 2025 report lists calcium as high as 39.4 parts per million. Calcium alone at that level works out to about 98 milligrams per liter of hardness, which the USGS scale calls moderately hard. For any other town, call the water department and ask for the hardness in milligrams per liter or grains per gallon. If the answer is 121 or more, which is about 7 grains, use Rheem's six-month schedule.

MWRA disinfects with monochloramine, and Canton does the same. Brockton, Whitman, Abington, Hingham, Avon and Sharon report using chlorine.

Two things do change it. If the house has a water softener, A. O. Smith and Bradford White both say the anode is used up faster, so have it checked more often. And if you are on a private well and only the hot water smells of rotten eggs, Bradford White traces that to bacteria in the water reacting with a magnesium anode. The fix is an anode made of a different metal. It is not to take the anode out.

A pan, an alarm and a shutoff

Massachusetts requires a pan under any heater of six gallons or more that sits above occupied space, such as one in a second-floor closet. A heater on a basement slab does not need one.

In a basement, a battery leak alarm on the floor beside the tank tells you about a leak while it is still a puddle.

An automatic shutoff goes a step further. A sensor at the base of the heater closes a valve on the cold line when it gets wet. A. O. Smith's manual tells owners to install one. The EPA's WaterSense program notes that some insurance companies give discounts or credits for leak detection systems. Ask your agent.

Know how old it is

A. O. Smith and Rheem put the life of a tank at about 8 to 12 years. The serial number gives the year yours was made. Past that age it is worth getting a price before it fails. What a replacement costs.

A plumber can check the anode, flush the tank, test the relief valve and read the pressure in one visit.

If water is already on the floor, start here.