I didn't know where it was but the previous owner had pointed out roughly where it was to me, so I took the man there. We looked for 5 minutes but could find nothing, We then went to another area of the garden about 75 metres away. where I vaguely thought it might be but I was feeling fairly silly by this time. After another five minutes I'd found nothing and the water man was looking elsewhere. I went to see if he'd had any luck.
He had a pair of metal rods about 50cm long with a right angle bend in them in his hands and told me he'd found a water course but not yet the meter hatch. I followed him for about 50 metres as the rods dictated and then into some rough ground where the rods suddenly swung round to cross each other. With a bit of scrabbling round with a spade, there was the meter under a small concrete hatch at the confluence of several pipes.
I asked is he did this regularly and he said yes, if there was a problem finding the water meter, as if you knew where the course of the water was, obviously the meter would be along there somewhere.
He also said that it worked most easily in calm and quiet conditions.
I'd often heard of water devining but thought of it as a kind of 'alternative' thing, never of it being used in this matter of fact 'tool for the job' way.