Toyota Highlander 2002 -- water accumulates under the carpeting

My son drives this car while in college and working at his internship. When he periodically comes home we notice water under the carpeting. You can press down on the carpeting and hear the water slosh in/out of the padding. If you open the drain plugs, immediately below, you can push some of the water out by pressing on the carpeting/padding. Usually it collects right in front of the back seats as there is a vertical riser that the seats are sitting on as there is no other place for the water to spread to. When very wet, the carpeting will also be damp under the front seats and the floors of the driver & front passenger.

Has any one had a similar issue and if so, where did you find the source of the problem?
Thanks in advance for sharing your suggestions.

Water leaks are common, and unfortunately difficult to track down. Several possible sources:

Air conditioner: have the A/C drain line blown out with compressed air. If clogged, condensate from the A/C won’t drain out of the car but will instead drip into the cabin.

Windshield seal: Rainwater can leak through a faulty windshield seal.

Sunroof: Have the sunroof drain lines cleaned out. If clogged, water inside the sunroof pan will overflow behind the plastic trim and leak down into the carpet.

Body panel sealer: Body panels are sealed with caulk-like sealant at the factory and sometimes develop pinhole leaks. Pull up the carpet under the dashboard and check for leaks along the seams at the corners where the firewall meets the side of the car.

Usually the leaks are so small that you can find the source only by looking in the right place under the carpet or plastic trim while someone outside the car sprays it with a hose.

Here’s someone with an '02 Highlander who found their leak source in the sunroof drain tube:

Good luck!

If it is on passenger front most likely ac drain. Very common issue for bugs to make nests and plug the tube.

I have blown out many an ac drain tube. Cheap and easy fix.