Outdoor backpacks certainly need to be waterproof
However, the backpack is not waterproof by its fabric stitching, etc., and it is waterproof, and when it has a rain cover, it is waterproof.
Of course, brands like birds and kitty hawks have waterproof backpacks, but they are expensive. And the rain cover is already able to cope with many situations.
If you mean waterproof, you should need a diving bag, but the diving bag generally does not have a professional carrying system, and it is not suitable for outdoor activities such as hiking and climbing.
