If the water is only occurring on the driver side of the vehicle, then the problem is the drain tube seal at the firewall. Normal repair for this is to remove the dash and AC box to replace the seal. This is very time consuming and very expensive however, so there is a faster repair that Mitsubishi has adopted to take care of this.
When this seal goes bad, it allows water to enter the driver side floor two ways: driving on wet roads water will enter, and driving the AC on, AC condensation will re-enter. Picture trying to pour water out of straight glass, how some of the water always runs down the side of the glass. This is what happens to the drain tube, some of the water runs down the side, and when the seal is bad, it runs back into the car.
What you need to do is apply an additional seal to the drain tube from the outside of the vehicle, eliminating the need for dash etc removal, and thereby cutting the costs considerably. Most shops will charge about 1 hour labor to perform this (around $100).
If you or someone you know is handy and flexible, this something you can do yourselves.
You will need to remove the air intake hose from the engine (10mm hose clamps on either end, and one small hose to pull off the center)
You will need to remove the upper strut brace (if equipped). That is the long bar that bolts to both strut towers and the firewall.
Once out of the way, look down the firewall by where the steering column comes through the firewall. The firewall insulation has a corner 'flap' in this location you will need to tear off or pull/fold out of the way.
Behind the flap you will see the AC drain tube coming through the firewall (and likely some foam seal sticking out around it.
To repair this we will need a pliable butyl rubber packing. I recommend 3M WindoWeld Ribbon Sealer (NOT liquid sealer)
Taking the sealant in 1-2 inch lengths you will need to fish it down to the drain tube and pack it around it, filling the gaps between the tube and firewall. This takes some dexterity and flexibility due to the distance down and the hood being in the way of your body while reaching down there. Take your time and be patient until you have the packing around the perimeter of the tube. It should look like a 'volcano' when done, with the butyl packing transferring smoothly from the tube to the firewall.
Once this is done, you will no longer have water problems on the driver side floor.