Just as there is no vest, which guarantees 100% bullet resistance, the same there is no backpack, which would be able to stay dry under a constant pressure of water. A good solution in such moments is matched case which perfectly protects a backpack and its contents.
Due to the wide range of colors, you will choose very quickly the camouflage that interests you. Kayaking, a trip in a downpour, or snow blizzard may turn out to be much less problematic especially when you have to make sure that the moisture does not reach the backpack. Come, see and read.