2 Answers

Wood absorbs moisture from the atmosphere or from the subfloor it is laid on, this  will usually cause it to swell and sometimes cause damage. I used to fit flooring as my trade and I once had to lay wooden flooring on joists which had 2 feet of water underneath, it was a contract that the owners insisted they could not wait for the floor to dry out. It was a large room approx 500 sq mts,the outcome was that the wood swelled so much that it pushed against the side wall and made it give way, it was the clients own fault for not listening in the first place, made me laugh.Wooden flooring should only be laid in a dry well aired room, and should be stored in that room for about 5 days prior to fitting.

http://www.coswick.com/hardwood_floor_care/moisture