This could be from the A/C evaporator drain if it's occurring when using the A/C, a water leak if it happens after it rains or a leaking heater core (leaks anytime). If the heater core is leaking you'll smell a "sweet" smell inside the car and the windows may fog up.
Thanks for the answers. The car with the problem in question is at college 3 hours away.I have asked to be aware of the distinct wet spot or absence of under the car when ac has been used. To keep a check of the dampness level indicating that it may be external since its been raining but now stopped and to remove the floor louever run the ac and look for the obvious. Any other suggestions?