We have a new (4 years old) house on a slab that has a mysterious water leak. After half a dozen plumbers and two leak detectors, the source of the leak cannot be found. Water pools and floods part of the main floor of the house. If the water to the house is shut off, or if the water heater is shut off, the flooding stops. The water coming up is clean, and there doesn't appear to be any water spots along any of the walls leading down to the floor. Has anyone else seen this, or have any pointers on how to find the source of the leak? Thanks!