What should I do if my tap water looks wrong after a burst main?

Water mains are lined over decades with iron and manganese deposits that sit undisturbed until the flow changes direction or speed. A burst, a repair, a valve operation or a hydrant being used reverses the flow and lifts all of it into suspension, which is why discolouration usually arrives suddenly and affects a whole street. The water company has a legal duty to supply wholesome water, and reporting discolouration is how they know where the problem is.

Safety

What you'll need

• Your water company's emergency number
• A clean white container or a glass, for judging the colour
• Bottled water for drinking, until it clears (optional)
• A washing machine filter and tap strainer to check afterwards

Step by step

1. Fill a glass and let it stand for a minute.Milky or cloudy water that clears from the bottom upwards is dissolved air coming out of solution. It is completely harmless and needs nothing done. Water that stays cloudy, or leaves a deposit at the bottom, is sediment.
2. Run the kitchen cold tap gently, not fully open.That tap is normally fed directly from the main. A slow steady run for a few minutes draws the disturbed water through without stirring up more. Blasting it at full flow makes it worse.
3. Stop if it has not cleared in about 20 minutes.Continuing to run it wastes water and can pull more sediment through from the main. Ring the water company and let them flush the network — that is their job and it is free.
4. Do not use hot water or the washing machine while it is discoloured.Drawing discoloured water into the hot cylinder or the combi means it stays there. Iron-stained water also permanently marks light laundry, and this is one of the most common compensation claims after mains work.
5. Ring the water company and report it.They will tell you whether there has been work in the area, whether other properties are affected, and whether any notice is in force. If several houses report it, they flush the main.
6. Treat black, oily or chemical-smelling water as a stop.Do not drink it, cook with it, bathe in it or give it to animals. Ring the water company's emergency line straight away and say exactly what you can see and smell.
7. Follow any boil water or do-not-drink notice exactly.A boil notice means bringing water to a rolling boil and letting it cool for drinking, brushing teeth, washing food and making up feeds. A do-not-drink notice means boiling will not help and you use bottled water.
8. Check the filters and strainers afterwards.Sediment blocks the strainers on tap outlets, the washing machine and dishwasher inlet filters, and the shower head. Clean them out once the water is clear, or the low flow will persist.
9. Keep evidence if it stained anything.Photograph the water, the marked laundry and the date. Water companies routinely compensate for damaged laundry and for supply failures under their guaranteed standards scheme, but they need to be told.

Tips

• The tap to judge water quality by is the kitchen cold tap. Every other tap in the house may be fed from a storage tank in the loft, where debris, insects and warmth make the water unsuitable for drinking anyway.
• If only your house is affected and the street is not, the problem is inside your boundary — an old iron pipe, a storage tank, or your own plumbing rather than the main.
• Blue-green staining on basins and baths is copper from pipework, usually with slightly acidic water. It is a plumbing question, not a mains one.
• A private supply — a borehole or spring — after heavy rain is a completely different risk, because surface water can carry contamination straight into it. Those need testing by the local authority rather than a water company call.
• Keep a few litres of bottled water in the house. Supply interruptions from a burst main are the most common utility failure in the UK and last hours rather than days.

Common mistakes

• Running every tap in the house at full flow — It draws large volumes of disturbed water through the property, stirs up more sediment in the main and fills the hot cylinder with it. One cold tap, gently, is the correct approach.
• Putting a wash on while the water is brown — Iron-stained water permanently marks light-coloured fabric, and a full load can be ruined. Wait until it is clear, and photograph anything that was affected.
• Assuming boiling makes any bad water safe — Boiling deals with microbiological contamination. It does nothing about chemicals, fuel or heavy metals, and concentrates some of them. A do-not-drink notice means exactly what it says.

If it doesn't work

Questions people ask