Check under the carpet, water may be coming up from the ground while youre driving. there may be several holes under the carpet near the pedals where wires and/or your pedal levers go through that should have some type of rubber grommet in them. perhaps some fell out
look under the wiper cowl, when i had water on my drivers floor the water was leaking through a crack there. simple fix once i had removed the wipers and the cowl with a bit of window urethane. and if you remove the carpet from your car and take it to a car wash most of the dirt and stains will come out with a bit of carpet cleaner and the power washer.