Does water only appear in the car when its rained? I think you have two problems, coolant pipes do not have any access to the passenger rear footwell unless you have parked uphill, but you still would have water in the front passenger footwell.
Is it a 5 door? If it is take off your door card and see if the plastic sheeting is intact with no rips, this is the door membrane. There must be a good seal of the plastic sheet to the door frame, if there isn't this could explain water in the passenger footwell.
As for loosing water over 30miles, I'd check your engine bay for leaks or signs of coolant drying on hot parts and leaving white stains! Then get a coolant pressure test done. If its 1l over 30 miles, top up the coolant, run the engine and i would think you would see it spray out from somewhere
