"Nervous O'Toole" wrote | ....Which is going to be a pain, and I am hopefully moving in a | few weeks. I live in a ground floor flat, and it has a huge void | under the floor. For the last few weeks I have heard a noise in | the kitchen which sounds like water running through the pipes.
As Set Square suggests, it may be water running through the pipes and running out elsewhere. Other than dripping taps check ball valves in WC and cold water tanks if you have them - it may be the WC cistern is continuously filling, but never gets to overflow level because it's flushed regularly.
Rather than ripping up floors it may be a lot easier to lift a corner of carpet in each room, drill a half-inch hole (which probably won't even need to be filled afterwards if carpet is going over) and look down using a borescope (from big hire shops), to see where the pipes run and if there are any signs of puddles.
Owain