My 97 Catera has standing water from a recent rain in the area beneath the cabin filter. Is there a drain hole at the bottom of this well that could be stopped up? I see a rubber stopper, but no hole.

rain water runs down the windscreen into a chamber that is drained past the front wheels inside the mudguards. For water to get into the heater box there has to be a blockage in the hoses from this chamber or a rust hole in the chamber into the cabin area.

I am not sure if it is the same problem I had with my '04 93 SS, but there is a cabin air filter that has a drain next to it that allows the rain water to run down to the ground. Mine was clogged up with leaves and other junk which caused the rain water to leak through the filter into the cabin. Being that yours is a different body style, your filter may be on the drivers side which would cause this. I would try to look up where your Cabin Air Filter is and try to clean the drain.

there are none. you either have a bad heater core or your air conditioner drain hose is clogged. It should be draining above the shock on the passenger front side.

If it is just water start with the AC, if it has coolant in it then its the heater core.

A leaking windscreen,door seal or window seal. Run a garden hose over your car and use baby powder to pin point where the water is in running from.

Yup;
Go in the engine compartment where the wiper parks on the passenger side, right ahead of the glove box. Pull back the rubber strip that is at the top edge. There is a plastic shield under the wiper and it comes off. Inside you will find the cabin filter. Remove the cabin filter (could use a change) and you will probably find the bottom plugged with leaves and debris. The drain hole is plugged allowing water to accumulate and pour into the passenger side foot well. Clean this out really good and run a snake wire down the drain hole to clear it. Then hose it down to wash the debris out.
Make sure you dry your carpets out really good by raising them off the floor board. The under pad once soaked, will stink the car up and rot your floors.

open doors and look for drain holes try sliding a wire into holes does it go in easily? if yes they check door seals for torn of loose seal, is there a sunroof/moonroof does this leak? get in car and have someone hose for awhile and look for leaks with a flash light? if door drian holes are blocked remove panel and clean inside. have you been using a/c? if yes is the a/c drain line blocked and condensation is leaking into cabin, also the front windshield has a grate at bottom remove grate and check channel for blocked drains or leaking seal. good luck on this one of these should be your problem.

HI. This will occur if the heater core has ruptured(leaking). This will allow for the transfer of coolant onto the passenger side floor. Replacing the core will solve this issue.

Look under the passenger side of the dash, behind the carpet. Feel the back side of the carpet for dampness. If so, try this: In the same area, look for a black rubber hose that comes from the heater plastic box, and pokes thru the firewall. See if it is plugged up. This is the drain pipe for the AC box, and the cowl panel if the side drains are plugged up. Try that, and please get back to me.

Dirt under the battery. Remove the battery-plate(metal) and clean up in the bottom hole. Beacuse of the dirt in the hole the rain water stand still and after a while the water start to find its way to the cabin of the car. You cant fix it in 5 minutes.

You need to clean out the cabin filter drain tube. The cabin filter housing allows the air to enter the cabin through the HVAC system. When water gets in here, the drain tube allows it to escape. If the drain tube is plugged with leaves and dirt, the housing fills up and it overflows into passenger floor area.
Remove the filter, clean the drain tube (prepare to get your feet wet) and put in a new filter.
The filter is below the pass side WS wiper under the plastic cover.