It is best to look for water leaks when everything is dry. First is the door seal or door, damaged in anyway? (I have seen the seat belt having damaged the door seal.) Does the door close flush with body? Ensure the door seal makes good and uniform contact with the door, pull back the carpet in the passenger's foot well. Sit in the passenger seat ( you may need a flashlight) get a friend with a garden hose to spray water around the passenger door jam to determine if the water is entering the doorway. Then spray water around the windscreen moving around the circumference of the windscreen. look around the windscreen area and look up from the floor mat area (as best you can)to determine if water is leaking in around the windscreen seal. Is there any rust around the windscreen area or is or a blocked drain? If you determine water is definitely coming past the door seal, clean and dry the seal and door jam, try smearing the seal with a smear of Vaseline (petroleum jelly) and retest with water from a garden hose. A final thought could water be coming up through the floor pan as you drive through water on the road?