Every now and then look take a look under cabinets with plumbing fixtures.  Plumbing fixtures underneath a sink can wear out with age and develop leaks. If left untreated, water damage will emerge in the form of mold and/or rot on wooden surfaces. 

The owner of this home was away overseas and the caretaker only checked on the upstairs rooms.  When the owner returned the entire basement was completely infested with mold from a water intrusion. The entire basement needed to be gutted and remediated.