Water Problem

My son has a 1995 Chevy S10 2wd pickup. He has been having a problem with a leak on the drivers side every time it rains. At first we thought the door seal might be bad but we tested it with a garden hose and found no evidence of any water. We also waited until dark and used a high beem flashlight to look for gaps or holes and again found none. I need some help or suggestions

Thanks
Bob

Pull the door sill interior trim up.Then pull the carpet back and dry up the floor.Shut the door and hose the outside down again.Look for where the water is coming in and trace it.Take more stuff out of the way if needed till you find the leak.To rule out a windshield leak take a blow gun that is hooked to a air compresser,spray around the outside of the windsheild with windex,hold the blow gun up to the inside of the windshield and blow around the outer edge of the windshield,if you see air bubbles come out on the outside of the windshield,there is the leak.You can also do this on the back window.