Why Is My Tap Water Cloudy or Milky?

Cloudy or milky tap water is almost always tiny air bubbles trapped in the water, and it is not harmful to health¹. The bubbles get in when a pipe bursts, when a main is repaired, when the water warms up in your pipework, or when a faulty tap washer draws air in¹. The water is safe to drink, and it usually clears on its own.

To check, fill a clear glass and leave it to stand for a few minutes. If the cloudiness clears from the bottom upwards, it is trapped air and nothing to worry about³. If it clears from the top downwards, or does not clear at all, the cause is more likely to be in the mains or your plumbing, and you should contact your water company⁵.

Most cases clear within 24 hours³. If yours has been cloudy for longer than a day, or your neighbours are affected too, ring your supplier and ask them to investigate⁵.

What causes milky or white tap water

Air gets into the water supply in several ways. The Drinking Water Inspectorate, the regulator for drinking water quality in England, says white or cloudy water is likely to be caused by air trapped in the water and is not harmful to health³. The same guidance lists the common triggers: a burst water main, reinstatement of a main after work on the network, cold water pipes warmed by heating or hot water pipes, a partially shut external or internal stop tap, or an aerator fitted to the tap³.

WaterSafe, the plumbing assurance scheme, adds that the air often follows a burst pipe or a faulty plumbing fitting¹. Affinity Water says water warming in the pipework causes naturally dissolved air to come out, and that a faulty tap washer can draw air in². Southern Water notes that disturbances or changes within the network can trap air in the system, which causes bubbly or cloudy tap water⁶.

In Scotland, the Drinking Water Quality Regulator for Scotland gives the same explanation: the usual cause of cloudy or milky water is air dissolved in the water supply, and when pressure is released by turning on a tap the air comes out of solution as many tiny bubbles¹⁰.

The bubbles are harmless. WaterSafe states plainly that cloudy water caused by tiny air bubbles is not harmful to health¹, and Bristol Water describes it as completely harmless⁴.

The glass test: clears from the bottom up

The test is simple and you can do it at the kitchen sink. Fill a clear glass with water and leave it to stand for a few minutes¹¹. If the cloudiness clears from the bottom to the top, it is just trapped air and nothing to worry about¹¹. The Drinking Water Inspectorate describes the same check: pour water into a glass and watch it clear from the bottom up³.

Several water companies give the same instruction. South Staffs Water says the glass should clear from the bottom upwards as the air bubbles rise to the surface¹². Affinity Water says the water should clear from the bottom up, which shows it is air¹³. Scottish Water says you should see the air clear from the bottom up as the bubbles rise to the surface¹⁴.

The direction matters. Air bubbles rise, so the water clears from the bottom first. If a glass clears from the top downwards, that points to something else in the water, and Cambridge Water advises contacting your water company in that case⁵.

It should clear within 24 hours

Most cloudy water is short lived. The Drinking Water Inspectorate says cloudy water should normally clear within 24 hours³. Southern Water says water that looks white, milky or contains bubbles is harmless and should naturally clear within 24 hours⁶. Dwr Cymru, the water company for Wales, gives the same figure¹⁵, and Severn Trent says the bubbles should clear naturally within 24 hours¹⁶.

Thames Water gives a shorter timescale for the network itself: any white water in the mains should clear within two to three hours¹⁷. Bristol Water notes that if there is lots of air after work on pipes, it can make the water look white or milky, and this usually clears within a few days⁴.

While you wait, there are things you can do to speed it up. The Drinking Water Inspectorate says if the problem has been present for less than 24 hours, run the tap to help clear the water³. Yorkshire Water suggests running your tap for 5 minutes, and if that does not clear it, running the tap again while turning the internal stop tap on and off several times to release air from the pipes¹⁸. Northumbrian Water says you do not need to flush your taps; just leave the water to stand for a minute or two and the bubbles should clear⁹.

When only your home is affected: stop taps, washers and pipes

If the cloudiness is only at your taps and your neighbours are fine, the cause is probably inside your home. The Drinking Water Inspectorate says persistent cloudiness that runs clear after a few seconds each time, or that lasts longer than 24 hours, may indicate internal plumbing is the cause³.

Start with the stop taps. The Drinking Water Quality Regulator for Scotland says if only your household is affected, check that the internal and external stop taps are fully open, as throttled taps can restrict the flow and aerate the water¹⁰. Bristol Water gives the same advice⁴.

Next, the tap washer. Affinity Water says a leaking tap washer can cause cloudy water, and you may hear a whistling sound when you turn the tap on; replacing the washer is the fix¹³. The same guidance says if running the tap for a short time clears the cloudiness, you may need to lag your hot or cold pipes².

Lagging matters because cold pipes can warm up. Yorkshire Water says if cold water pipes touch unlagged hot water pipes, the cold water can warm up and become cloudy¹⁸. Bristol Water says lagging your water pipes should help to minimise warming and transfer of heat⁴. The Met Office adds that good quality lagging protects pipes from freezing, helps insulate your hot water system and saves you money²¹.

Still cloudy after a few days? Check your plumbing

If the glass test points to air but the cloudiness keeps coming back, work through the possibilities in order. Affinity Water suggests asking whether running the tap for a short time clears the cloudiness; if it does, you may need to lag your hot or cold pipes, and if taps are dripping or the flow changes solve the problem, try replacing the washers².

Yorkshire Water lists faulty plumbing in your home as a cause, and says if the company is not working in your area, you should get an approved plumber to come and check what is going on¹⁸. Severn Trent says if you still get cloudy water after taking these steps, you could contact a local approved plumber¹⁶.

An approved plumber is one signed up to a recognised plumbing assurance scheme. WaterSafe runs the national register of approved contractors in the UK¹.

If the problem is not in your home, it is in the mains, and that is your water company's job. Wessex Water says if the cold water kitchen tap is affected and your neighbours are experiencing the same issue, there could be a problem with the water mains, and you should contact the company to investigate⁷. Yorkshire Water says contact them after trying running the tap, turning the stop tap, asking neighbours and checking for work in the area¹⁸.

Cloudy water after a burst main or other work

Cloudy water is common after an interruption to your supply, such as a burst water pipe¹. The Drinking Water Inspectorate lists a burst water main and reinstatement of a main after work on the network as triggers for white or cloudy water³. Southern Water says after repairs you may notice your water looks cloudy; this is harmless and can usually be cleared by running your tap for a couple of minutes²².

Southern Water gives the same reassurance for work on the network: cloudy water after repairs is harmless and can usually be cleared by running the tap for a couple of minutes¹¹.

If you are on a private supply rather than the mains, the same principles apply, but the responsibility for checking and fixing the supply sits with you rather than a water company.

Cloudy water after flooding

After a flood, it is natural to worry about the water. Belfast City Council's emergency planning guidance says mains tap water should not be contaminated after flooding²². The fire and rescue service advises contacting your water company if tap water is discoloured or tastes bad²³.

Milky water after flooding is usually aeration. The Chartered Institute of Plumbing and Heating Engineering says milky-coloured tap water after flushing is probably due to turbulence in the water mains causing aeration, and if you leave the water to settle in a glass it should clear after a few seconds²⁴.

If your water is cloudy for any other reason after a flood, or if it is discoloured rather than milky, treat it as a possible contamination issue and ring your supplier. For more on what to do when supplies are affected by flooding, see our guide to flooding.

Drinking cloudy water

If the glass test shows the cloudiness is air, the water is safe to drink. Essex and Suffolk Water states that cloudy water caused by air bubbles is safe to drink and not harmful to health⁸, and Northumbrian Water gives the same assurance⁹.

If you want to clear it before drinking, leave it to stand for a minute or two and the bubbles should clear⁹. South Staffs Water suggests running the kitchen tap and slowly opening and closing the inside stop tap a couple of times to release trapped air in the internal plumbing¹².

If the water is cloudy and does not clear, or if it is discoloured rather than white, do not assume it is safe. Contact your water company and follow any advice they give. For the wider question of whether your tap water is safe, see Is Tap Water Safe to Drink?.

Neighbours affected too? When to ring your water company

If your neighbours' water is cloudy as well, the cause is likely to be in the mains rather than your plumbing. Cambridge Water advises contacting your water company if your water has been cloudy for more than a day or so and your neighbours are also affected, or if a glass of water clears from the top downwards⁵. Wessex Water says if the cold water kitchen tap is affected and neighbours have the same issue, there could be a problem with the water mains, and you should contact the company to investigate⁷.

When you ring, have these details ready:

• How long the water has been cloudy
• Whether it affects all taps or just one
• Whether the glass test clears from the bottom up or the top down
• Whether neighbours are affected
• Whether there has been recent work or a burst main in the area

If your supply has been off, our guide to what to do when your supply comes back on covers the first steps, and how to report no water or a burst pipe explains how to get through to your supplier quickly.