Cameron wrote:

Hi there. I just moved into a new home and got hit with an incredibly
enormous water bill. I checked my water meter and could see the little
dial moving - not all the time but every 10 seconds or so it would
move forward. Sometimes it moves backwards but never enough to make up
for the forward movement. I have made sure all water is off in the
house and have done visual checks for leaks as well as a dye test in
the toilets. I called a plumber over and he said this motion is caused
by the expansion tank on my water heater.

SNIP

The whopper bill could have been due to some billing fluke
during the transfer of ownership. As Joe said, take that
up with the utility. And see what the next reading is.
Or, take your own readings, day-by-day.

I cannot think of any reason why the exp tank would cause
meter movement every 10 seconds.
I'm not doubting that it stopped when he closed off the
exp tank, but it doesn't add up yet.

I think I'd start by measuring daily consumption.
If you can, make a measurement over a long period when no one
is at home (and no water being used).

Jim