Hyundai i20 wet seat

Hi guys, my Mrs car has got wet rear seat and I have no idea on where to look for a leak. The weird thing is where it is. The seat is stained on the part your back leans against and about 12 inches long behind the driver right at the bottom. It's a 3 door car so can't be door related. I checked the rear window but no signs of water been running down or anywhere near the rear window. 1 thing we did notice is when we lifted the carpet in the boot there was small puddle just behind the seat so obviously the seat has absorbed the water and gone through the front. I've even checked the rear window and didn't see any signs of water and again the rear window wouldn't explain the location of the small puddle. There is no dampness on the roof either. Does anyone know if maybe the washer pipe is on that side? Just a wild guess? Cheers.