Why is my water cloudy, discoloured or smelly?

Three simple tests — which taps, hot or cold, and what happens in a glass — separate almost every case into harmless, temporary, or something that needs attention.

What you'll need

• A clean clear glass
• A few minutes

Step by step

1. Fill a glass and watch it settle.Milky water that clears from the bottom upwards over thirty to sixty seconds is dissolved air coming out of solution. It is completely harmless and usually follows work on the mains.
2. Check whether it is hot, cold or both.Cold only points at the incoming supply. Hot only points at the cylinder or the boiler. Both points at the supply into the house.
3. Check whether it is one tap or all of them.One tap means that fitting or its supply pipe. All taps means the incoming main or the whole system.
4. Run the cold kitchen tap for a few minutes.For brown, orange or rusty water, running the tap that comes straight off the main usually clears it within a few minutes as the disturbed sediment passes through.
5. Ask a neighbour.If they have it too, it is the mains — often after a burst, a hydrant use or scheduled work. Your water company's website usually lists current work in the area.
6. Treat hot-only discolouration differently.Rusty hot water in an older system points at a corroding cylinder or steel pipework. It is not a mains problem and will not clear by running it.
7. Investigate a rotten egg smell in hot water only.That is usually sulphate-reducing bacteria in a hot water cylinder, associated with stored water kept too cool or a sacrificial anode reacting. Running the cylinder up to 60 degrees for an hour often clears it.
8. Investigate a smell from all taps and drains.If the smell is present at every tap including cold, and around the drains, it is far more likely to be a drainage smell in the room than something in the water.
9. Check for a black rubbery deposit.Black flecks in the water usually come from a perished washer or flexible hose liner. Check the aerator gauze at the affected tap.
10. Call the water company if it persists.Discoloured cold water that does not clear after running for several minutes, or any taste or smell of chemicals or fuel, should be reported. They will test it.
11. Do not drink it while you are unsure.Use bottled water for drinking and cooking until you know what it is. Aerated cloudiness is safe; unexplained discolouration is not something to guess about.

Tips

• The glass test is the whole diagnosis for cloudiness — clearing bottom-upwards means air, staying cloudy means particles.
• Only the cold tap directly off the main is a valid sample. A tank-fed or filtered tap tells you about the tank or the filter.
• Report anything you cannot explain. Water companies would far rather test a sample than not know about a problem.

Common mistakes

• Assuming cloudy water means contamination — The overwhelming majority of cloudy water is dissolved air, released as mains-pressure water reaches atmospheric pressure. It clears from the bottom up in under a minute and is harmless.
• Running every tap for a long time to clear brown water — It wastes a great deal of water and can pull more sediment through. Run the cold kitchen tap gently for a few minutes; if that does not clear it, phone the supplier.

If it doesn't work

Questions people ask