Wet n Windy

Various companies like Surfpro (sp?) have exactly what you are looking for. These are companies that specialize in smoke and water restoration. Check your phone book and ask them.

I have seen a sensitive electronic listening device with thru headphone output and a stethescope type probe used to detect in slab leaks by sticking the tip of the probe thru the carpet and against the slab. Sorry I do not remember the company name though.

If the carpet gets wet, (and maybe even if it doesn't,) why don't you try IR photography?,Problem is, that this must be done at a very early stage of the leaking.

Other possibility is ultrasonic detection, There are zillion companies making this type of equipment.

Wangito

Did you try a megohmmeter? (like what is used to test motor insulation)