Water in body of car

I can hear water under the floorboard of my front passenger seat. It sloshes around when I accelerate quickly, brake quickly or take a sharp turn. It’s also keeping the floor wet - only on the front passenger side and under the seat. I can’t figure out where the water is coming from or how to get it out of there. Any ideas?

Your AC or heater box drain is plugged or the windshield is leaking on that side. There could also be water in the bottom of the passenger door. Look at the bottom of the door to see if the drains are open and the plugs have been removed. The water is under the carpet and needs to vacuumed out. You will need to lift up the carpet on to get it dry.

Thanks! Will it take removing the dash to get these drains unplugged? Or can I get to it from the engine? Would fixing something like this mean taking it to my mechanic or can I do it myself?