Why Your Hot Water Smells (And how to fix it)
Why Your Hot Water Smells (And How to Fix It)
If your hot water has developed an unpleasant smell — often described as rotten eggs or sulphur — you're not imagining it and it's not a sign the water is unsafe to drink. But it is worth fixing. Here's exactly what's causing it and what you can do.
What Causes the Smell?
The rotten egg smell is caused by hydrogen sulphide gas, which is produced when sulphate-reducing bacteria in the water react with the magnesium sacrificial anode rod inside your hot water tank. The anode rod is designed to corrode slowly to protect the tank from rust — but it can react with certain water chemistries to produce this sulphur smell. The problem is more common in areas with high mineral content or water that sits in the tank for extended periods.
Why Does It Only Affect the Hot Water?
Because the bacteria thrive in warm, standing water — exactly the conditions inside your hot water storage tank. The cold water supply doesn't have this problem because it doesn't sit at warm temperatures. If both your hot and cold water smell, the issue is likely with your water supply itself rather than your hot water system, and you should contact your water authority.
How to Fix It
The most effective fix is to replace the magnesium anode rod with an aluminium or zinc alloy anode, which doesn't produce the same reaction. In some cases, flushing the tank and treating it with a small amount of hydrogen peroxide can resolve the problem temporarily. Your plumber can assess the situation and recommend the right solution. In older systems, this is also an opportunity to check the overall condition of the tank.
How to Prevent It
Having your anode rod inspected and replaced every 5 years is the best prevention. Keeping your hot water system set to at least 60°C also kills the bacteria that cause the smell — as well as preventing legionella. If your property has been vacant and the hot water hasn't been used for an extended period, running the hot water through all taps for a few minutes before use is a sensible precaution.
Hot Water Smelling Off?
Our licensed plumbers can diagnose the cause and fix it fast. Serving Penrith and the Blue Mountains.
