Water damage can come from condensation, leaky roofs, burst pipes, seepage, etc. Many types are obvious, as is the damage caused by them. But even if you can’t see the damage, a little water can often be worse than obvious leaks. Left untreated, it can cause:
Structural rot damage
Foundation damage
Electrical hazards
Mold
Foul odors
Pipe corrosion
Repairing hidden water damage can be a challenge. Depending upon the source of the damage, it may or may not be covered by homeowner’s insurance. In the case of mold, getting rid of the problem may be a monumental undertaking.
I don't have x-ray vision, but I have experience with moisture issues, and know a lot about how, where, and what to look for in this regard. My electronic moisture meters are a great help in locating adn assessing moisture problems.