The AC evaporator drain hose probably exits through the floor pan, just rearward of the firewall. You may be able to see it if you pull the front passenger carpet back. The hose would go from the evaporator housing down through the floor. Sometimes, the hose is clogged, and sometimes, the hose is mis-routed or disturbed when installing stuff like aftermarket audio systems, security systems, etc. If the hose is mis-routed, it often gets pulled out of the opening in the floor pan and lets the condensate drain under the passenger carpet.
Another possible source of water is a missing underbody plug or clogged sunroof drain.