Because water buckets can be stored in an equipment spot rather than in the inventory, it gives people an insanely large water supply that they can access at any moment while only sacrificing one hand rather than a great deal of inventory space.
I love running around with my bucket, but I feel like it trivializes things like water skins when I can just lug it around while foraging instead of making other expensive means of storing water in the inventory.
I think that carrying a bucket of water should limit your movement speed to a walk (or a crawl if the devs happen to be sadists) or maybe limit it to a crawl with a walk costing stamina.
Sorry fellow bucket runners
