You need a new heater core.
in the front of the engine, by the water pump
On a 1997 Nissan Altima the water pump should be mounted on the front of the engine. It is right at the thermostat housing.
on the front of the motor behind the fan
you will find ECM center front (inside car ) on the floor hide by black plastic.
in front of radiator,its connected to your fan blade.
in front of your engine under your cam cover
The source of the water is probably from faulty or failed window seals surrounding your front & rear windsheilds.
Front top of the intake manifold.
I hav e the same problem
Heater Core is the likely culprit
It is under the center stack in the center of the front center/dash area. Basically, on the floor directly below the stereo.
JUST FOLLOW THE FAN BLADE AND YOU WILL FIND IT ON THE FRONT OF THE MOTOR