dpb wrote:
Hustlin' Hank wrote:
...
Air in water lines that are on city water can be a common occurence,
especially if you are at the end of the main line. When the pumps
loose power due to an electrical outage, or other reason, air is
produced thru what is called "cavitation" in the pumps volute. If this
is the case, there is not much you can due about it, other than
contacting your water company and see if they can (or are willing) to
either reduce the pressure slightly or take other measures. They way
want to know about your problem in order to maximize their delivery
and avoid other problems. Anyway, check with them before you call a
plumber.

What a bunch of mostly hooey...

And, even if it were, air in supply lines would show up in both hot
_AND_COLD_, not hot only...

--

The OP said there are bubbles in the cold, but not as many. Suppose the
incoming water is saturated with dissolved air. If it stands in
cold-water pipes in the house that are warmer than the source, bubbles
will form. Even more will form in the water heater. Households using
more water might not notice it.

I imagine water wouldn't have that much air unless it was dissolved
under pressure. Could a municipal water system dissolve air in water
under pressure? Another possibility is that the dissolved gas was
generated in the pipes as a product of water purification. Could that be?