"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

Robert