Open the hot tap and the sulphur hits immediately. That thick, unmistakable rotten egg stink that fills the room and makes everyone pull a face. The cold tap runs clean. No smell at all. Only the hot side.
A rotten egg smell hot water produces almost always traces back to one component inside the tank that most homeowners have never heard of. The sacrificial anode rod. It sits inside the tank doing an important job but in certain water conditions, it creates a chemical reaction that produces the gas responsible for the smell.
Here is what the anode does, why it causes the problem and what to do about it.
What the Anode Rod Actually Does
Every storage tank is steel. Steel rusts. The sacrificial anode corrodes instead of the tank walls. Made from magnesium or aluminium, it is more reactive than steel so the water attacks it first. The tank stays protected as long as the anode has material left.
Without an anode, the tank corrodes within a few years. With one, it lasts 8 to 15 years. Essential for the tank. But also the primary trigger for a rotten egg smell hot water tanks in certain areas develop.
How the Anode Creates the Smell
The chemistry is straightforward.
As the anode corrodes, it releases hydrogen. Australian water contains trace sulfate. Sulfate-reducing bacteria in the warm tank feed on that sulfate. The hydrogen accelerates their activity. Their waste product is hydrogen sulfide gas, which dissolves in the water and stinks when the tap opens.
Three ingredients. Sulfate. Bacteria. Hydrogen from the anode. Remove one and the smell stops. Cold water does not smell because it never sits in a heated tank with a corroding anode.
Why Magnesium Anodes Are the Worst Offenders
Most tanks ship with magnesium. It is highly reactive, corrodes fast and releases more hydrogen. More hydrogen means more bacterial food and a stronger smell.
A new tank with a fresh magnesium anode can develop the rotten egg smell hot water owners notice within weeks. Not every tank does. It depends on the water chemistry. Some supply zones have enough sulfate to trigger it. Others do not.
The Three Anode Options
Magnesium anode.
The standard. Highest corrosion rate. Best tank protection in most water conditions. But the most likely to cause the rotten egg smell. If the water chemistry triggers the reaction, magnesium is almost certainly the source.
Aluminium anode.
Corrodes more slowly. Releases less hydrogen. Provides adequate tank protection in most conditions. Significantly reduces or eliminates the smell in the majority of cases. The most common swap when a rotten egg smell hot water issue is diagnosed.
Switching from magnesium to aluminium is the fix most plumbers recommend first. It is affordable, takes about 30 minutes and solves the problem in most homes.
Powered anode (impressed current).
Does not corrode at all. Protects the tank using a small electrical current instead of sacrificial corrosion. No corrosion means no hydrogen. No hydrogen means no bacterial food source. No bacteria means no gas.
A powered anode eliminates the smell permanently. It costs more upfront than a standard anode but it lasts the life of the tank and never needs replacing. For homes where the water chemistry makes the smell persistent regardless of anode material, powered is the definitive solution.
When to Check the Anode
Most homeowners never check the anode. It sits inside the tank, out of sight, doing its job until it is fully consumed. By then the tank walls start corroding and the system is on borrowed time.
Recommended anode inspection schedule:
- First check at 3 to 5 years after installation
- Every 2 to 3 years after that
- Immediately if a rotten egg smell hot water develops
A plumber checks the anode by shutting off the water and power, partially draining the tank and removing the anode through the fitting on top. If more than 50 percent of the rod has corroded away, it gets replaced.
Replacing the anode before it is fully consumed extends the tank life and gives the opportunity to switch from magnesium to aluminium or powered if the smell has been a problem.
Other Factors That Make It Worse
The anode is the primary trigger but a few other things amplify the problem.
Low thermostat setting.
Bacteria thrive between 40 and 55 degrees. A tank set below 60 gives them ideal conditions. Raising the thermostat to 60 kills most of the sulfate-reducing bacteria.
Stagnant water.
Tanks left idle for days or weeks let bacteria multiply unchecked. Holiday homes and vacant properties develop the strongest smell after periods of no use.
High sulfate water.
Bore water and some regional supplies carry more sulfate than treated mains water. More sulfate means more bacterial food regardless of the anode type.
Sediment in the tank.
A layer of mineral buildup at the bottom of the tank creates a warm, sheltered environment where bacteria colonise more easily. Flushing the tank clears the sediment and reduces the bacterial population.
How to Fix It
Start with the simplest measures and work up.
Flush the tank.
Clears existing hydrogen sulfide and reduces bacteria. Temporary fix but gives immediate relief.
Raise the thermostat to 60 degrees.
Kills bacteria. Run the taps for a few minutes after the tank reheats to clear the old water.
Replace the magnesium anode with aluminium.
The most common permanent fix. Reduces hydrogen production. Stops the bacterial chain reaction in most cases.
Install a powered anode.
The permanent solution for persistent cases. No corrosion, no hydrogen, no smell. More expensive but lasts the life of the tank.
Chlorinate the tank.
A plumber flushes the system with chlorine to kill bacteria. Effective immediately but temporary if the anode stays the same.
A rotten egg smell hot water produces is fixable. The anode is usually the cause. Changing it is usually the answer.
Do Not Remove the Anode
Some homeowners remove the anode entirely. The rotten egg smell hot water produced stops because hydrogen production stops. But the tank loses corrosion protection. Steel walls rust from inside. Tank life drops from a decade to a few years.
Removing the anode trades a smell problem for a corrosion problem. Always replace it with an alternative rather than leaving the tank unprotected.
Get It Checked
A rotten egg smell hot water keeps producing does not resolve on its own. The bacteria grow. The smell gets stronger. The anode keeps corroding.
One plumber visit sorts it. Inspect the anode. Flush the tank. Swap to aluminium or powered. The smell stops. The tank stays protected. The showers go back to normal.
The anode is a small part doing a big job. When it creates a side effect, the fix is changing it, not ignoring it.
About Us
At Campbelltown Hot Water Systems, we provide fast same-day hot water repairs, replacements and installations across Campbelltown. With over 30 years of experience, our fully licensed team works on electric, gas, solar and continuous flow hot water systems. If your hot water has a rotten egg smell, poor temperature, leaks or stops working, we can inspect the system, check the likely cause and recommend the right repair or replacement option with clear advice from the start.