What can cause a pool of water on a floor board?

Sounds like a water leak from one of various possible locations. I would suggest the following checks in this order: 1) If there is a moonroof, check moonroof drains to ensure they are attached properly and clear of restrictions. 2) Has a windshield been replaced ever? If so, it's possible that windshield sealing is incomplete, cracked and damaged, or missing. 3) Body seams could be cracked or damaged. Has there ever been body damage? www.repairpal.com/repair-shops