In article ,
Bob Minchin writes:
SantaUK wrote:
We just had two guys going round our cul-de-sac lifting all the incoming
water mains covers and sticking a pole down the hole, and listening into a
big sucker on the other end. What are they listening for?

Yes, quite likely. You can hear quite low water flow in pipes.

Leaks generate white(ish) noise, which tends to be identifiable.
You can attach two microphones to two different points on a pipe,
detect the phase shift between them, and work out exactly how far
the leak is on the pipe from the microphones. Saves digging up a
whole pipe just to find it.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]