Cloudy hot water: air, scale or sediment?
One glass and two minutes tell you whether it is air or something worse. Here is how to read it, and where to stop.
Cloudy hot water is usually air, and air is harmless. Fill a clear glass from the hot tap and watch it. If it clears from the bottom up within a minute or two, you can stop worrying. If it stays milky or leaves a layer at the bottom, read on.
| What you see in the glass | What it usually points to | Who deals with it |
|---|---|---|
| Clears from the bottom up | Tiny air bubbles in the water | Nobody. It settles on its own |
| Cloudy hot, clear cold | Something in the hot water system or its pipework | A licensed plumber if it persists |
| Cloudy hot and cold | The mains supply or a recent works event | Your water utility |
| White flecks or grit that sink | Scale or sediment | A licensed plumber |
| Cloudy at one hot tap only | That tap, its aerator or its cartridge | You can check the aerator |
Air is the commonest cause
Water under pressure holds dissolved air. Heat it and it holds less, so the air comes out as fine bubbles when the water reaches the tap. That is why hot water can look cloudy even when cold looks fine.
The glass test settles it. Bubbles rise and the water clears from the bottom. This is more noticeable in cold weather and after any work on the mains.
Run the cold tap as a comparison
Fill a second glass from the cold tap. If both are cloudy and both clear the same way, your hot water system is a bystander. The air or sediment is arriving from outside.
Ask a neighbour. If theirs is cloudy too, it is a supply event, and your water utility is the right call. The cloudy water from the tap guide covers that side in more detail.
Cloudy hot only: look at the system
If the cold is clear and only the hot is cloudy, the cause sits between the cold inlet of your system and the tap. Two suspects matter most.
The first is scale. Hard water leaves mineral deposits in a storage tank, and a disturbed layer can cloud the water for a while. Our hard water guide explains why some areas see it far more than others.
The second is sediment. Any storage tank collects a layer at the bottom over the years. A pressure change, a supply interruption or a service can stir it up. If the cloudiness is improving each day, that is the likely story.
When it is not worth chasing
A one-off cloudy glass after plumbing work or a street repair is not a fault. Run the hot tap for a few minutes and check again the next day. If it has cleared, do nothing.
Do not drain or flush the tank on a hunch. Draining a hot water system is licensed work, and it rarely fixes air.
The checks that are yours to make
- Do the glass test. Does it clear from the bottom up?
- Compare hot and cold. Is the cold clear at the same time?
- Try other hot taps. If only one is cloudy, unscrew the tap aerator and rinse it.
- Ask a neighbour. A supply event shows up next door too.
- Note how long it lasts. Days of improvement and weeks of no change are different problems.
What to tell the plumber
- Does the glass clear from the bottom up, or does it stay cloudy?
- Is the cold tap clear at the same time?
- How long has it lasted, and did anything happen first?
- How old is the unit, and is your water hard?
How far can you take this yourself?
The glass test, the comparison and the aerator are yours. Everything inside or around the unit is not. Your state or territory plumbing regulator licenses and inspects that work, and the licensed work pillar sets out where the line falls.
Frequently asked questions
Why is my hot water cloudy but my cold water clear?
Hot water holds less dissolved air, so the air comes out as tiny bubbles at the tap. Fill a clear glass: if it clears from the bottom up, it is air and harmless. If it stays cloudy, the cause may be scale or sediment from the hot water system, and a licensed plumber should look.
Is cloudy hot water safe to drink?
Cloudy water that clears from the bottom up is only air. Water that stays cloudy, smells or tastes wrong should not be drunk. Contact your water utility or your state health authority, and have a licensed plumber check the hot water system.
How long does cloudy hot water take to clear?
Air clears in a minute or two in the glass. Cloudiness after street works or a supply interruption usually settles within a day or two once you run the taps. If it has not improved after several days, get it checked.
Should I drain my hot water tank to fix cloudy water?
No. Draining a hot water system is licensed work in Australia, and it rarely fixes cloudy water caused by air. Run the hot tap, check again the next day, and call a licensed plumber if it persists.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Australian Government, energy.gov.au. Hot water systems — types, installation and energy performance
- NSW Fair Trading. Plumbers, drainers and gasfitters — licensing