Most likely it's water condensation from the AC and the drain tube is blocked. From under the car you should be able to find a small tube or hose coming out the firewall on the passenger side. It could be damaged or most likely just clogged up with stuff. Stick a vacuum cleaner hose to it, might be enough to clear it. Poke it out with a soft wire if needed. Run the AC and it should start dribbling out within a few minutes, the more humid it is the faster and more it'll dribble.