We have determined to a high degree of certainty that there is a substantial water leak (about 6l/minute) in the concrete slab of the house we live in.

The 2 fairly clueless contractors my completely clueless landlord has dragged in so far, have little to offer to resolve the situation. The second guy wants to write off the existing pipes and recreate the entire indoor plumbing above ground.

In the West there are companies who can isolate a slab leak to within a few inches, by using specialized listening devices. I wonder if this is available in Thailand, particularly in Phuket. Any referrals would be greatly appreciated.

What is slab leak?

Did you mean a leak in the water pipe that is concealed in wall or floor slab? Or a leak in a water retaining structure or flat roof slab?

I'm assuming our OP has a leak in piping either in or under his floor slab.

Question is, even if you locate the leak do you (or your landlord) want the hassle / expense of digging up the floor (try finding matching tiles)?

Standard fix is invariably to isolate the area where the leak is and run external pipes

Try this method,still used by water companys in UK,even saw it being used in pattaya 2 weeks ago,guy tracing leaks on 3rd road Pattaya.

Thanks guys, for the feedback so far.

Here is what I'm actually looking for:

https://youtu.be/U3hdoRrnqw0