Water leak when it rains on drivers side floor board

Do you have a sunroof? If you do then more then likely the drain is clogged. If you do not then you have a seam that is opened up on the firewall.

You will need to remove the cowl panel and start water testing to find where the water is coming in. I attached the process for removing the cowl panel.

To water test this, you want to place a hose on the windshield so that the water runs down the front of the vehicle and then start looking on the inside up under the dash to try and find where the water is coming in. You can pull the carpet down without removing it. You just want to find where it is coming in because you are going to seal it from the outside.

Once you find where it is coming in you want to use what is called a flowable sealer. This will feed down into the crack and seal it. I attached a picture of the product. Using this product will prevent you from removing everything in the way to access it. Clearly you want to get it as close as you can but it will flow down and find the opening. Let us know what questions you have. Thanks