A heater producing smelly water is an everyday problem we have all encountered. There is hardly a person who has never come across the notorious rotten egg odor that heaters tend to produce sooner or later. It results from the reaction of anaerobic bacteria which lives in the water inside the heater and the magnesium or aluminum of its sacrificial anode (i.e. the metal rod in the heater tank which protects it from corrosion). The suggestions below will, hopefully, help in removing this noxious odor.
Removing the Sacrificial Anode Is Not a Solution
Some people may suggest that you remove the sacrificial anode. This will indeed solve the problem but is bad advice. Removing the anode will create a new problem: your heater tank will quickly rust to such an extent that it will become practically unusable.
Some people may also tell you to replace your magnesium anode with an aluminum one. Don't bother, for aluminum is no better than magnesium in the "rotten egg smell" removal department.
Step 1 - Pour Hydrogen Peroxide in the Heater Tank
Close the cold water valve to your heater and turn on a hot water faucet to reduce the pressure in the heater. Open the heater tank and pour 1 liter of hydrogen peroxide in it (you may also use chlorine bleach, but the peroxide is safer). If the smelly water comes from one basin only, you do not have to put detergent in the tank; simply pour it in the respective basin.
Step 2 - Replace the Magnesium Anode
The above procedures are only temporary solutions. If you want the real deal, you will have to replace the magnesium anode with one from aluminum-zinc alloy. It is the addition of zinc that will chase away the rotten egg smell from your heater tank.
Heater anodes are either of the hex-head or the combo type. A hex-head anode is usually installed at the top of the tank and you will be able to see it quite easily (although, it may be hidden behind a plastic cap or the sheet metal insulation).
A combo anode is mounted in the hot-water-outlet port. Try to run a screwdriver down the port; if there is an anode in it, the screwdriver will not go down more than 2 inches. Both types can be either of standard or flexible make (unlike standard anodes, the flexible ones are grounded down to the core wire). Be sure to identify the kind of anode in your heater before you replace it. Also, some heaters have not one, but two anodes. If you want to eliminate the odor completely, replace both of them.
Step 3 - Install Power Anodes
Sometimes, however, simple anode replacement may not be enough. This is particularly the case if water has been softened (water softening increases anode consumption). So, you can try installing powered anodes: they do not use aluminum or magnesium and are, therefore, a sure guarantee that the smell will go away. Moreover, they will not need replacement. Keep in mind, however, that these anodes are several times more expensive than the regular ones.