The Water Bolt is a spellbook obtained randomly by collecting books in a Dungeon. Every time the player uses a Hammer to destroy one of the books in the dungeon, there's a chance the book dropped is the Water Bolt.
It casts a slow moving projectile that bounces off of walls and passes through enemies, inflicting 15 base damage as it goes. The bolts seem to have a very long duration. Each use costs 20 Mana.
Due to the ricocheting nature of the bolts and it's ability of multiple hits, this weapon is superb in caves, homes, or the very dungeons it's found in. A good way to use this against a boss is to build a closed corridor of any material and lure the boss into it, then letting multiple Water Bolts bounce around.