Urgent Issue

Smelly or Foul-Tasting Hot Water

Hot water smelling like rotten eggs, sulphur, or mould? Bacteria growing inside your storage heater is the likely cause. Find out why it happens, how to confirm it, and what to do — with same-day service available across Singapore.

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What to Do Right Now

1 Do not drink or cook with the smelly hot water
2 Run the cold tap — if cold water also smells, the issue is in your supply pipes or building tank, not the heater
3 If only the hot water smells, the source is inside your storage heater
4 Increase thermostat to 60°C — sustained high heat kills most bacteria (temporary measure only)
5 Call for a professional flush, disinfection, or replacement assessment

Common Causes

Sulphur-reducing bacteria (SRB) growing in a storage tank set below 55°C

Degrading magnesium anode rod reacting with bacteria to produce hydrogen sulphide gas

Stagnant water in a storage heater that has not been used for several weeks

Bacterial biofilm forming inside tanks with heavy sediment build-up

Legionella bacteria risk in tanks consistently kept below 50°C

Smelly Hot Water — Why It Happens and What to Do

A rotten egg or sulphur smell from your hot water tap is one of the more alarming water heater symptoms — and for good reason. It almost always indicates bacterial activity inside your storage heater tank. Unlike a mechanical fault, bacterial contamination raises genuine health concerns that make prompt action important.

How to Confirm It’s the Heater

Before calling for service, do this quick test:

Run the cold tap for 30 seconds. Smell the water.
Run the hot tap separately. Smell again.
If only the hot water smells — the problem is inside your storage heater. This guide applies.
If both taps smell — the issue is upstream in your building’s supply pipes or roof tank. Contact your property manager or PUB directly.

What’s Causing the Smell

Sulphur-Reducing Bacteria (SRB)

The most common culprit. Sulphur-reducing bacteria naturally present in water supplies can colonise storage heater tanks when conditions are right: water temperature between 20–45°C, low flow (infrequent use), and sediment providing a surface for biofilm to form.

These bacteria convert dissolved sulphates in water into hydrogen sulphide gas — producing the unmistakable rotten egg smell.

Degrading Anode Rod

Most storage heaters contain a magnesium anode rod for corrosion protection. As this rod degrades, it can react with certain bacteria to amplify hydrogen sulphide production. In some cases, switching to an aluminium/zinc anode rod reduces the smell significantly.

Legionella Risk

Legionella pneumophila bacteria — the cause of Legionnaire’s disease — can colonise storage heater tanks kept consistently below 50°C. Singapore’s warm ambient temperatures accelerate bacterial growth. While true Legionella risk in a domestic hot water system is relatively low, it cannot be dismissed — particularly for elderly occupants or those with respiratory conditions.

Legionella cannot survive water temperatures above 60°C. This is why 55–60°C is the recommended thermostat setting for storage heaters.

What Happens Without Treatment

A mild bacterial smell can escalate to full biofilm contamination over weeks. Sediment layers at the tank base provide an ideal environment for bacteria to multiply, even if temperatures are raised. Once a significant biofilm establishes, flushing alone may be insufficient — full tank replacement becomes the only reliable solution.

Our Recommended Fix

Tank flush — removes sediment and stagnant water where bacteria concentrate
Disinfection — chlorination treatment to kill active bacterial contamination
Thermostat recalibration — set to 60°C to prevent regrowth
Anode rod inspection — replace if degraded; switch to aluminium/zinc if magnesium anode is contributing to the smell
Tank assessment — if biofilm is established, advise on repair vs. replacement

Call +65 8888 1111 or WhatsApp us to book a same-day inspection. We service all storage heater brands across Singapore.

Affected Heater Types

Storage Water Heaters

Primary risk — stagnant warm water is ideal for bacterial growth

Gas Storage Water Heaters

Same bacterial growth mechanism as electric storage heaters

Frequently Asked Questions

Why does my hot water smell like rotten eggs?

A rotten egg or sulphur smell in hot water is almost always caused by hydrogen sulphide gas produced by sulphur-reducing bacteria inside the storage tank. These bacteria thrive in warm, stagnant water — particularly in tanks running below 55°C. The magnesium anode rod can accelerate the smell by reacting with the bacteria. A professional tank flush and disinfection is required, along with thermostat recalibration or anode rod replacement.

Is smelly hot water dangerous to use?

You should not drink or cook with foul-smelling hot water. The sulphur smell itself is not directly toxic, but bacterial contamination — including Legionella bacteria — is a genuine health risk, particularly for elderly users, children, and anyone immunocompromised. Switch off the heater and book an inspection before continued use.

Can the smell come from my pipes rather than the heater?

Yes. If your cold water also smells, the source is in your building's supply pipes or roof tank, not the heater. Contact your property manager or PUB. If only the hot water smells, the heater is the source. You can confirm this by running both taps and comparing the smell.

How do you fix a smelly storage water heater?

The fix depends on the cause. A professional tank flush removes sediment and stagnant water. Disinfection treatment kills bacterial contamination. If the anode rod is degraded and contributing to the smell, it can be replaced ($80–$120). Thermostat recalibration to maintain 60°C prevents bacterial regrowth. In severe cases with heavy biofilm build-up, tank replacement may be recommended.

How can I prevent the rotten egg smell from returning?

Set your storage heater thermostat to at least 55–60°C — bacteria cannot survive sustained heat above 55°C. Annual servicing including tank flushing and anode rod inspection prevents sediment build-up and detects bacterial growth early. Avoid leaving the heater off for extended periods without running it periodically, as stagnation accelerates bacterial growth.

Need Professional Help?

Our licensed technicians can diagnose and fix your water heater issue quickly. Same-day service available across Singapore.

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