As noted, be sure it is not coolant from leaky heater core. If water, then it is due to clogged condensate drain - passes through firewall near right frame rail where bottom of heater/fan housing is.

The reason that the drain clogs is that leaves and stuff gets in the top due to the leaf screen becomming disloged.

The way to fix everything is to remove the cowl piece between the hood and windshield. A couple of bolts along the forward edge under the rubber seals and hooks at the sides onto some blind rivet studs and along the front edge of windshield with clips.

Inside the intake plenum you will find the screen usually stuck to the bottom of the cavity with sealing putty - you need to remove it and re-fasten it to the underside of the cowl grill. THere is also a second screen that goes over the entrance to the heater box along with a plastic shield - these also need to be replaced in proper position. But before you put everything together, get the heater cleaned out as best you can. I usually use an air hose nozzle to blow stuff back through the drain. Then remove the blower motor from inside (it is probably toast anyhow due to the water) and continue to clean out everything as best you can. Note that there was a service bulletin to attach a small drain hose to the drain outlet to direct the drainage down past the frame.

When re-installing the new blower motor, be sure to attach the small tube to the motor housing correctly.

For further details, there was an article in Shade Tree Mechanic column in Rolling on this job (Nov/Dec 2000).