water, water every where

[Ackattack]

I started to take out the interior of the GMC to repair the floor pans in the cab. I was surprised to find a lot of water on the floor on the passenger side. Plus the water on the drivers side.

On the passenger side it's where your left foot would be. I'm thinking the water might be coming in through the ventilation system (not coolant though, like a heater core leaking).

On the drivers side it's below the handle for the parking brake realease.

Any ideas or experience on what to look for to stop it from leaking would be great.

Thanks guys!