On Tuesday, October 24, 2017 at 10:21:52 PM UTC-4, Lenny Jacobs wrote:
On 25-Oct-17 1:35 AM, dpb wrote:
On 24-Oct-17 9:16 AM, trader_4 wrote:
On Tuesday, October 24, 2017 at 8:10:54 AM UTC-4, dpb wrote:
On 24-Oct-17 2:37 AM, Lenny Jacobs wrote:
...

I did check the faucets. I noticed that the water pressure dropped.
However, I did not wait until all the water drained. That would have
taken a while.


Until you do, you can't show that isn't where the water's going...what
type of isolation valves are installed?

--

+1

Not sure one has to wait for all the water to drain.Â* If you open the
highest faucet on each apt, there should be nothing to drain.
...


Good point; particularly with a multi-level/multi-unit facility.
Isolate; then if there's a drip at the uppermost level that doesn't stop
you know the isolation valve isn't holding perfectly.

Didn't say how many units but a small bypass flow over several could add
up to a measurable amount in toto at the meter; still the cycling
phenomenon has to be related to some mechanical system somewhere it
would seem.

I suppose there is that outside chance the OP raised of a external
pressure source that is cyclic and the difference in flow be pressure
related...that could be checked by inserting a pressure gauge in that
line but such rapid cycling would not seem to be likely for a supply
system characteristic I would think of unless there's some sort of other
large industrial facility or the like that has such a demand; the
overall system pressure would be more nearly constant.

--

Didn't think of bypass flow. However, if there is no leak, the bypass
flow won't go anywhere and the meter should not run. I'm sure faucets
and toilets don't leak.

Another thing I noticed after the first post is that if I shut off the
main valve for few hours then turned it back on, I could hear water
gushing through the pipe. That indicates the pipe was empty, right?
Can I assume that the pipe from the main valve to the lowest toilet
valve (faucet valve is always higher than toilet valve if on the same
floor) is at least partially empty? If that assumption is good, that
would indicate at least one leak is between the main valve and the
lowest faucet valve.

Agree, that would indicate that the water is somehow leaving the pipe
on the apt side of the shutoff valve. If the leak was in the supply
line entering the house, before the valve, when you turn it back on
after awhile there should not be the sound of water rushing in to fill
the pipes. It sounds like whatever is leaking or taking the water
not only takes whatever is leaking past the shutoff valve, but also
some of the water that's already in the pipes. Which would suggest to
me that whatever it is, it's more likely on the lower levels. If you
had something leaking at the highest faucets I don't see that partially
draining the pipes when the shutoff valve is off.