The cause of rotten egg odor

The most common cause of smelly water is anaerobic bacteria that exist in some water and react with the magnesium and aluminum sacrificial anodes that come with most water heaters to produce hydrogen sulfide gas, making the classic rotten egg odor. The problem is most common in well systems, either private or municipal.

Softening can make smelly water much worse.

What not to do to get rid of smelly water

We've heard of plumbers or handymen advising people to remove the sacrificial anodes from their water heaters as a solution to smelly water. It's a solution all right, but one that will ensure your water heater rusts out in record time. There is a reason why removing an anode voids the warranty.

Additionally, people have been told to replace a magnesium anode with an aluminum one. Don't. Aluminum causes just as many rotten eggs as magnesium.

This won't fix stinky water forever, but it's a start

Cheap, simple, effective, but not forever. Shut off the cold water valve to your water heater, open a hot faucet somewhere in your house to relieve pressure, drain some water from the tank, open the plumbing on one side, and dump in a few pints of hydrogen peroxide. Close everything up, turn on the cold water again, and let some water run from all spigots and taps. You should be odor-free until the next time you go out of town and allow the water heater to sit, unused. Then you'll have the problem again. For details on this procedure, go to Know-how.

By the way: use peroxide, not chlorine bleach. Either will work, but peroxide is much safer.

One caveat: if you have smelly water at one sink, but not all of them, dump the peroxide down the basin overflow, instead of into the water heater. Sometimes bacteria can build up in there, too.

The complete fix, in most cases ...

Very often, replacing the standard magnesium or aluminum anode rod with an aluminum/zinc alloy anode will solve the problem. The zinc is a key ingredient, since pure aluminum anodes will also reek to high heaven.

For most folks, an aluminum/zinc anode is the cheapest fix for this problem and we urge you to try it first before considering the alternatives. Unless you soften your water. More on that in a moment.

Contrary to our usual advice, we do not think you should put two anodes in your tank, even aluminum/zinc ones, as it may worsen the odor.

These anodes come in four flavors: standard hex-head, flexible hex-head, standard combo, flexible combo.

Those terms, doubtless, mean nothing to you, but they're important if you're to choose the right anode.

The photo at right shows hex and combo anodes. The latter is also called an outlet anode.

Hex-heads go in their own hole on top of the water heater. In most cases, you'll be able to see the hex head. If you can't, the anode is either hidden under the sheetmetal or your tank has a combo anode.

Combo anodes share the hot-water-outlet port. If you're not sure if there is an anode in there, run a long screwdriver down it. If there is an anode, the screwdriver won't go more than a few inches.

Some water heaters have two anodes. Not only is it important to put an aluminum/zinc anode into the heater; it's also important to remove all previous anodes or the hot water will still smell.

... but, if you have soften

We have had a few people buy an aluminum/zinc anode and the odor didn't go away. That's vexing for them and us. The cases involved softened water. Softening can speed up anode consumption by increasing the conductivity of the water. That can increase the amount of hydrogen sulfide gas produced.

So we've started offering powered anode rods. A sacrificial anode creates an electrical reaction inside a water heater as it corrodes. A powered anode does the same by feeding electricity into the tank. Since there is no magnesium or aluminum, there's no smell. We don't recommend them for everybody, though, because they're several times more expensive than sacrificial anodes.

One more thing: There are several configurations of residential water heaters. Most have a hex-head anode in its own port somewhere on the top of the tank. A few do not. Some of Bradford White's, A.O. Smith's and State's residential tanks employ a combo anode/hot-water outlet/nipple in the hot port. A powered anode can be used with those tanks by adding a brass tee to the hot port. The bottom port of the tee will connect to the tank; the plumbing to the house will go out the side port; the powered anode will screw into the top port with the element hanging down inside the tank.

How do you tell if it's hex or combo? It's a fair question because some heaters do have a hex anode but it's hidden under sheetmetal, or perhaps under a plastic plug in the top. Visit Know-how for strategies on uncovering hidden anodes. The easy acid test though, for a combo, is to disconnect the hot-side plumbing and run a long screwdriver into the nipple. If it stops in just a couple of inches, there is a combo anode there. It's worth doing this test even if your tank has a hex anode because if there is a standard anode anywhere in the water heater, you'll have rotten eggs, no matter what anode you employ elsewhere. On the other hand, more recently, manufacturers have shipped water heaters with heat-trap nipples. On those, it may be necessary to remove the nipple to see if an anode is attached to it.

Anodes to eliminate smelly water

Pricey alternatives

There are a couple of other potential solutions you can consider. One is Rheem's Marathon electric heater, which is plastic-lined and has no anode. However, it costs several times more than a standard water heater and might be expensive to operate in some parts of the country where the utility rate structure favors gas.

Another is an instantaneous heater. We're not overly fond of those. They cost several times more than a tank-type heater and have their own problems. To see what we think is the downside, read Tankless. Still, this is one place where they might be a solution.

Why me, oh Lord?

There have been a number of situations where people replaced their water heater and found they had smelly water with the new one even though they didn't with the old one. All we can do is speculate on the causes. All the action in water heaters takes place where nobody can see and it never happens in a scientific laboratory testing environment.

It might be that toward the end of the life of a water heater, there was too little anode left to make much hydrogen sulfide gas. Or it might be the water supply changed in some way. Our own water heater once had smelly water and required an aluminum/zinc anode, and now it doesn't.

There's something few realize: water is a chemical and one that is constantly changing. The water that flows out of the tap this evening may be different from that from this morning, either because of what's in the ground or because water companies have changed their sources of supply or added something new to it..