I just fixed my water problem, the right front and rear floor area was soaking wet. I found that it was air conditioning condensation that was draining down the rear seat heat duct. It turns out that the drain was completely plugged with a small disc of glue or silicone rubber. I don't know how it got there but must have been from manufacturing years ago. Access to clean it was very hard. You have to remove the glove box, and blower motor. There are a bunch of screws holding the housing. I did not remove it, I just pulled it down a bit to clean the pluged drain. I also put some silicone rubber around the seal where the housing touches the body of the car. This is where the drain hole is.
If you have engine coolant in the water you have a different problem. Don't turn on the air conditioner for a while and see if the floor dries out. I had to use two rolls of paper towels to get all the water up. You would be surprized at how much water condenses.