Why is it always the HOT water that leaks?
That's because of the expansion and contraction of the pipe, as it heats and cools, rubbing against rocks, pebbles, concrete, and other pipes.

Are the pipes IN the slab?
No they are in the soil under the slab.

What is the best way to repair a leak?
If you can, always reroute the pipes. Once you get the pipes out of the ground your chances of any future leaks along that line are minimal.

Why don't I have any water showing up if I have a leak?
A lot of times the water from a leak will find an underground path to follow, such as the outside of a sewer pipe. As a result, that will take the water away from the area of the leak. Also, depending on the soil, the ground may absorb a lot of water before the area around the leak saturates and the water starts to surface.

My carpet is damp...what do you mean I don't have a leak?
Under natural circumstances you have moisture that "breathes" up through your slab and evaporates in to the air. You usually never notice this. If you have something that is creating a vapor barrier for this moisture, such as linoleum, plastic runners in your hallway or under an office chair, boxes or storage bins under beds or in closets; these will trap that moisture and not allow it to evaporate. When this occurs, the moisture absorbs into the carpeting or gets trapped under the flooring and will cause discoloration or dampness.