Robert wrote:

"The four smallest wheels of my water meter go
round OK when someone has a shower, but the ones that measure
whole cubic metres don't go round any more. So my usage is zero
every time the water company reads it. They don't seem to have
noticed. I expect someone will come around and have a look one day. "

I wonder what your legal position will be when they realise and then
present you with a large backdated estimated bill (or the equivalent
unmetered bill). Since you knowlingly allowed the situation to
continue you might end up worse off than if you get it fixed

Yes, I was considering telling them. But it's not really my
problem. The water company installed the meter which is now
faulty. Any sensible computer system should flag zero or negative
readings for attention. The water bills are paid automatically
from my bank account, so I simply glance at the bill and file it
and do nothing else. I am prepared to pay an amount based on my
usage for the last year. I'm just interested to see how long it
will take for them to notice.

If a utilities company has made a mistake, they tend to be
difficult to deal with, so it's best to avoid that.
The meter reader for my power company made a very large mistake
that implied my usage had doubled. Their computer system didn't
flag that either. When I phoned them, they wanted me to supply a
password for ID (when they had never given me one) then they
would not accept my reading and sent someone around to re-read
the meter.