There could be a number of reasons you are getting moisture in the wood floors. Collectively, the reason is from humidity of some sort. I can suggest one thing that worked for me when my wood floors were just starting to show signs of warpage and curling up to the point you can just see it  when the sunlight was just right:  IF you have a basement or crawl space (I have a basement)  I was told by a professional floor insataller to go in the basement and drill holes into the sub-floor UP TO THE WOOD FLOOR ONLY.  Do not drill through the wood floor.  I drilles 3/4 inch holes in  a lot of areas up through the sub-floor and stopped at the oak wood floors above the sub-floor.  It helped my floor lay back down!