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.
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.
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.
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.
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.
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