Tony Polson wrote:

I found electricity and telephone cables but could not differentiate
between them and water pipes, full or empty. All I knew was that I
had found *something", which we later dug up. In each case the
location was exactly as indicated by the dowsing rods crossing.

It's pretty straightforward to take a guess in an average house where
service cables might be located. Are you sure that you didn't merely
make a lucky guess ?

The crossing of "dowsing rods" is a well-understood phenomenon.