A photograph of a concrete floor inside a house. The floor has been dug up to reveal a corroded copper pipe running in a straight line very close to the surface.

Copper heating pipes laid into a solid floor, very poorly protected from reacting with the concrete floor. These pipes had corroded and leaked, resulting in dampness throughout the floor.

Source of water: the leaking pipes.

Repair: install adequately protected metal, or heat-resistant plastic, pipework.