Auto body repair & detailing: Rain water leaking into car, windshield area, rubber gasket

Question
Hi Expert, Thank you,

My husband has an 89 Civic 2-door, which leaks when it sits in the rain.  The water pools on the floor of the back passenger-side, but not elsewhere. We ran a hose over the car to try to determine the route of the leak-in or tributary action, but couldn't re-create the leak. Is it possible for rain water to leak UP from ground level? Seems counter-intuitive...

Any thoughts of things to try?

Thanks

Answer
Mikaling, this will test your detective skills and patience.You will find the leak;with water hose  [no sprayer on end]and low pressure start spraying  along lower body sides ,below window  level, spray into all openings IE  door lines, fender lines ,rocker lines, inside/under wheel openings front and rear splash area.  Check for leaks with a person  and flashlight inside car while spraying. No leak ,good ,next spray water around glass area  lower belt line area where glass  meets body .no leak good now do upper glass, upper door area do windshield area with lots of water .so far this will take about 45 min. of soaking with hose,no leak,good . Now do roof /sunroof area ,no leak good.Next open hood same spray go along firewall and windshield base area/air vent inlet. it could be the air conditioning drain  is plugged with stuff overflowing into passenger floor area. hard to dry out  must remove carpet and let it dry in the sun hang over a fence wash with clean water let drip dry .You don't want a mold problem .I never had a leak i could not find and fix.  
it takes time and patience. the fix is usually simple ;some caulk sealer or rubber gasket or seal or a door adjustment, or sunroof drains or inner door seal or speaker wire holes or.......
hope this helps,Bill Tuma