check membrane between door and trim panel,make sure it is intact and fully stuck to door on sides and bottom,if not it will allow water to enter vehicle wrong side of door seal!
k
March 2011
Yes i agree, it could be from the heater matrix which is like a small radiator that provides heat via the coolant which runs round the engine. Has your coolant level dropped? Another reason could be intake of water via bulkhead early ford escorts had a bad reputation for this.
rapidspec
March 2011
is it a vauxhall? i had a heater matrix located underdash behind gearnob, they can leak maybe?