It sounds like there's a leak in the heater core or in the hoses that attach to it. If you're not of a serious mechanical bent, it's time to take it to a shop.
It's not easy to replace a heater core, a major section of the dashboard has to be taken apart to get to it. If you let it go, the leak will eventually get so bad that it will cause overheating of the engine.
It is under the dash on the passenger's side.
On the Passenger Side, below the Alternator, by the Firewall.....
The reservoir is located on the passenger side rear of engine.
heater core may be leaking or hole in floor
install 3.8 Chevy impala crank sensor passenger side , remove wheel and use pully to pull out crank shaft
More than likely a burnt out window motor in that door.
Power steering pump reservoir. Back of engine passenger side.
On the Passenger Side, behind the Firewall, in front of the Glove Box. Remove the Kick Panel for access.....
The service port is by the Firewall, just below the Passenger's Side Windshield Wiper Arm Shaft.....
It's located at the edge of the trough on both corners on the outside of the firewall. It's a long line along the lines of the coolant leaks.
Passenger side floor board, where the passenger's feet would be just to the right, behind a cover.
on top of the passenger's feet untder the glove box has 2 5.5 mm bolts and 2 connectors coming out of it.