cloudy water from cold taps

[Robert]

For the last couple of days the cold water from our taps (direct from the mains) has been coming out of the tap cloudy. The cloud effect is caused by tiny bubbles which gradually fizz out leaving the water clear. There is no odour, colour, or bad taste so I presume its safe to drink but where have the bubbles come from and why? It is the same from all the cold taps bathroom and kitchen so I am sure the cause lies with the water company rather than at home (we have not done anything to the plumbing to have changed anything). Thanks.

[Tim Watts]

Robert wibbled on Sunday 14 February 2010 21:50

Have they bumped up the chlorine input for some reason?

[Peter Parry]

Perfectly safe.

Air. The water in the reservoir is cold and has a lot of dissolved air. In the pipe it is under pressure so the air remains dissolved. When it comes out of the tap the pressure immediately falls and the air comes out of solution and turns back into gas bubbles - exactly the same as opening a bottle of fizzy pop.

[geraldthehamster]

So, sparkling water at no extra cost?

Cheers Richard

[Chris Hogg]

We get this after the water company has been doing work on the mains supply pipes. Air gets into the pipes when they open them up, and when re-connected the air is trapped in the pipe (we're at the end of a mile-long uphill stub, which tends to empty when the main is opened and doesn't get flushed when they re-connect). When the water pressure is turned on, this air is forced into solution in the water, to re-emerge as fine bubbles when the pressure drops again, i.e. as the water exits from the cold taps, and making the water look white and opaque. It's just like a soda siphon but with air rather than carbon dioxide. As you've discovered, it clears fairly rapidly on standing as the bubbles coalesce and rise to the surface. As others have said, it's perfectly harmless and quite OK to drink. Like us, all your cold taps obviously run at mains pressure, rather than being fed from a tank in the loft.

[Andy Burns]

There should be a "wash-out" at the end of such runs to allow the water company to flush the system.

[Chris Hogg]

If such exists, it's not used. But I doubt its existence; we're right out in the country. Whenever the water 'goes off', we can expect an hour or so of explosive spluttering and coughing from the cold taps as the air is forced out under pressure. I sometimes fear for the joints in the pipes, it can be so violent; the 'rigid' mixer tap in the kitchen (i.e. not one on a flexible hose) physically recoils! We tend to flush the loos repeatedly to clear the air, as it seems to be less violent to do it that way. It also gets rid of any discoloured water.

[JTM]

I seem to remember that liquid (water) does not compress, whereas gas (air) can be fairly easily compressed. But inside the pipes, the air will be compressed until its pressure is equal to the water. When the compressed air reaches the open tap it just decompresses and expands as it is forced out by the water behind.

As the pressure of the air or water will not be more than that of the water, your pipes should be all right.

[John]

If the toilet ball valves are plastic they could get damaged!

I wonder if the Water Company should be made aware and whether they could fit some form of automatic air separator?

[Robert]

That's exactly what it look like.

Only the bath tap comes from the loft tank, I think.

Thanks for the reassurance.

[Chris Hogg]

It's not the static pressure that's the problem, but the extreme hammer effect that goes with these explosive discharges of compressed air from the taps.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Chris Hogg saying something like:

Same happens a lot to my supply. I've been meaning to make an air purger pipe for ages now.