Sulfur or "rotten-egg" odors can develop in water heaters and in corroded iron piping even if the water is chlorinated city water. This usually occurs if the water has a low chlorine residual, high levels of sulfates, and/or the water has sat inactive for days or weeks.

Odors Are Often Caused by Bacteria

The incidence of rotten egg odor or black water in water lines is due to the reaction of sulfates and microorganisms in water. To determine the source of the odor, it is important to check to see whether the cold water contains odor, or just the hot water.

Run the hot water to notice the odor. Then move to another faucet and run the cold water. If the cold water has an odor, then the source is in the cold water. If the hot water alone has odor, then the odor is occurring primarily in the water heater.

City water is usually chlorinated, which kills odor causing bacteria. However, in some cases the chlorine residual may be very low, particularly if your house is at the end of the distribution system and far away from where the chlorine is first injected at the water treatment plant. If you run your cold water and notice an odor, its best to call your local water utility and report the problem.

Even though the water entering a pipeline from the city water treatment plant can be free of odor, the water may develop odors directly in the distribution line. This can be caused by old iron distribution systems that provide an environment for the sulfate bacteria to grow. Increased bacterial growth depletes both the oxygen and the chlorine residual in the piping. By the time it reaches the house it can be free of chlorine residual and odors can easily develop.

Odors can develop even in cold water piping in the home, especially in galvanized iron piping. Often iron piping in the house is of an older age and can be corroded, providing a good environment for the bacteria to grow and odors to develop. If there is an odor in the cold water, and the source is chlorinated city water, its best to trace and see if the piping is iron piping, and then replace it with copper. As a first step to this process, one can chlorinate the piping and sanitize it, and see if the odor can be eliminated. If the odor returns, it may be necessary to replace the old galvanized iron pipe with copper piping.

Water Heater Odors

Most odors reported on city water, are from smelly water heaters. If your hot water has a sulfur or 'rotten egg' odor to it, the odor is being produced right in the water heater.

Almost all water heaters have “anode rods” which in a cathode-anode reaction, produce excess ions that wear off the anode rod and adhere to the inside glass lining of the water heater, preventing corrosion. The greater the activity of the anode, the greater the amount of hydrogen ion and hydrogen sulfide gas. If the cold water does not contain odors, but the hot water does, then a thorough sanitizing of the water heater tank will eliminate the odor.

See the procedure below. If you are not familiar with the functions of your water heater, DO NOT ATTEMPT this yourself. You can have this done by a licensed plumber to avoid damage to your water heater, or causing electrical problems, or gas explosions by improperly restarting the water heater if gas. We offer this information as informational and educational all, and no warranty or guarantees are expressed or implied.
If the water heater is old and corroded, cleaning the sediment from the water and sanitizing by chlorination could cause the water heater to leak.

Procedure for Chlorination of Hot Water Heaters to Eliminate Odors

1. Turn off the manual switch if the water heater is electric. For gas heaters, turn the control to Pilot. Make sure the pilot is still lit so you can restart the water heater when the procedure is completed.

2. Close the cold-water inlet valve at the water heater.

3. Open a nearby hot water faucet and the T&P (temperature and pressure valve, located on the top of the water heater) valve to relieve tank pressure. Note of caution: T&P valves may need replacing if defective or old.

4. Drain the water of enough water to compensate for the bleach to be added. Use a hose connected to the drain valve if an open drain is not adjacent to the water heater. Tip: have on hand a hose bib cap, available at any hardware store. When the procedure is completed, in some cases the drain valve will leak, and a hose bib cap can be screwed on the end of the drain valve, preventing the need for a drain valve replacement. Or replace the valve if desired with a new drain valve.

5. Remove T&P valve, anode rod, or disconnect the hot water outlet pipe from the water heater.

6. For best results and to preserve the life of your water heater, inspect the anode rod. If corroded, replace with a new aluminum/zinc anode rod, which will create fewer odors. Figure 3 Typical gas water heater cut-away showing anode rod and cold water dip tube.

7. Pour one gallon of household bleach, or ½ gallon of pool chlorine for each 30 gallons of water heater tank capacity. Use the T&P valve, anode rod or hot water outlet pipe opening to pour the chlorine in. Re-pipe the water heater and close the T&P valve.

8. Open the cold-water inlet at the heater and fill the tank with water. Observe the water level through the closest hot water faucet. Close inlet valve when the tank is full.

9. Leave the bleach mixture in the heater for one hour.

10. After one hour, open the cold valve again, open all the hot water faucets and allow the bleach mixture to clean the hot water supply pipes. Drain the remaining chlorine solution from the tank through the heater drain valve.

11. Close the heater drain valve, and completely fill the tank with fresh water. Leave the water in the tank for 15 minutes.

12. After 15 minutes, purge the hot water supply lines and drain the water from the tank though the heater drain valve, flushing out any sediment if present. Close the drain valve.

13. Make sure you purge all air from hot water lines from the open hot water faucets. Close the hot water faucet after all the air is out of the system.

14. Check for water leaks at all fittings used; repair as necessary.

15. Turn on the manual electrical switch, or turn the gas control knob back to “On” and verify that the heater burners have lit and turned back on.

16. Check for normal water heater operation.


If the Odor Returns to the Hot Water

After this procedure is completed, the odor will be eliminated in almost all cases. However, if it returns within a few weeks, then the chlorination procedure can be repeated. However, in many cases the cold water will still have problems with recurring odors due to continued presence of sulfate bacteria and low chlorine residuals in the water.


Other options for smelly sulfur odors in water heaters are:

• Remove the standard magnesium anode rod and replace with an aluminum or zinc anode rod if you haven’t already.

• Replace the water heater with a plastic lined water heater, or an instantaneous water heater, or a commercial stainless steel water heater (none of which have anode rods).


About Anode Rods

All glass-lined water heaters have sacrificial anode rods. This is a rod made of magnesium or aluminum, that's formed around a steel core wire, and is screwed into the top of the tank. Physically connected to the steel of the tank, it creates an electrochemical reaction, similar to that of a battery, whereby the anode corrodes and the steel remains intact. When there's no sacrificial metal left on the anode, the tank rusts out.

All metals fall somewhere on the galvanic scale, and the "nobler" ones will remain intact while the lesser ones will corrode. When steel and copper are touching, the steel will corrode while the copper remains intact. That's why dielectric unions are necessary on items like copper flex connectors.

Magnesium and aluminum are less noble than steel, which is why they're used for anode rod. The anode rod can be unscrewed and replaced, even though it’s difficult sometimes to get the old anode rods out sometimes. An anode's life depends on the quality of water, the amount of use the tank gets and the quality of the tank. If the water is aggressive or corrosive, the anode rods should be inspected yearly and replaced as needed.

Removing the Anode Rod

1. Close the cold-water gate valve

2. Turn the control to pilot if gas, or turn off the electrical power switch if electric water heater.

3. Remove the vent pipe to allow working room, a gas water heater.

4. Open a hot-water fauce to relieve pressure. If the hot water doesn’t stop running after you

5. Open a faucet in the house, then the gate valve cold-water shut off is not shutting off completely. At this point, turn off the main water line to the house and replace the valve if needed.

6. Let a gallon or so of water out the drain valve.

7. Locate the anode rod. On some tanks, the hex head of the anode is exposed and in sight. On others, it's hidden sometimes under a sheetmetal top that's foamed into place.

Remove the anode rod per the following tips:

In some applications, the anode rod is hidden beneath sheet metal, and one must drill through the sheet metal (not too far) and then use a screwdriver to feel around and find the hex head. The anode will most likely be on the backside of the tank, 1 1/2 inches out from the flue in a semicircle between the hot and cold ports.

Once it's found, drill another hole and use it as a start for cutting a hole with tin snips to give access to the anode. Be careful of the sharp sheet metal edges.

On some water heater tanks, there is no hex-head anode, just a combination nipple/anode/hot water outlet, shown on the right. You can determine this by disconnecting the hot-water side flex connector, and running a long screwdriver or similar implement down the nipple. If it stops after a couple of inches, it has run into the combo rod. Original anodes are not installed with pipe thread seal tape and they can be very hard to remove.

Take a 1 1/16-inch socket wrench and a cheater bar to put on the end of it to give maximum leverage, and loosen the anode.

The new anode rods are 44 inches long. Pulling out the old one can be accomplished by bending it if there is no headroom. A new one can in some cases be bent when installing and then straightened there is lack of headroom above the water heater, or you can get anode-rods that’s are.

In some cases you may have to use a segmented anode, which has been milled down to the core wire, which is soft. That allows the segments to be bent, inserted in the tank, and straightened out.

In some cases, if there is a vent, you can run the anode rod up the vent pipe and then back down.

If more than six inches of core wire is exposed, or the anode is splitting, replace it. Put the new one in with pipe thread seal tape to make next removal easier.

If you cannot get the old anode rod out, you can install a combination anode/nipple rod on the hot side. Disconnect the hot-side plumbing, remove the old nipple with a pipe wrench, and put in the new rod (with pipe thread seal tape!).

Galvanized steel nipples (left) will eventually rust and corrode, causing the nipple to plug up with rust. They may collapse if they need to be removed. It is better to use a plastic-lined dielectric steel nipple (right), which can't react with water or other metals