Water building up on floor inside

I suspect that your car has an air conditioning condensation drain pipe that comes out under the hood. It will be somewhere lower down, on the firewall (behind the engine). Sometimes these drains get clogged with junk and gunk. You can try sticking a pipe cleaner or screwdriver in there and clearing out the gunk. Otherwise, you will have to take the lower part of the dashboard off in order to get to it. It will take some work, but it is doable with basic tools (maybe a cheap wrench set or socket set and a couple of screwdrivers).

If that is not the problem, then the leak could also be coming from the heater core. Think of the heater core like a radiator. Coolant comes through it and the blower blows air across it, heating the air up, creating heat. When they start to leak, it usually ends up on your floorboard. So when the engine is cold, check your coolant to see if you are losing any.

Another place to check is if you have a sunroof. Those have drains that run down through the door pillars on many vehicles. Those can fail and dump the water onto the floor.
Which side is the water on? That can tell a lot.