i keep a lightweight plastic trash bag folded up in my saddlebag incase i park it ouside at a motel out of town for the night to cover the seat. the water will seep into the seams where the seat is sewn together so that's about the only thing you can do if it's a seat with vinyl upholstery, which most all harleys are, except for the cvo's i think. using a plastic trash bag tucked in around the edge of your seat when you're washing it will keep you from having that water from soaking into your jeans after you're done washing it too.