Water Bolt

The Water Bolt is a spellbook obtained on bookshelves in a Dungeon. They are able to be picked up the same way a potion is picked up (by right clicking). The sprite for the Water Bolt book always looks the same.

It casts a slow moving projectile that bounces off of walls and passes through enemies, inflicting 15 base damage as it goes. It moves in a straight path until colliding with something. The bolts seem to have a very long duration, shortened only by each ricochet it undergoes (normally 5 ricochets will end the bolt's life). Each use costs 20 Mana, because it can ricochet off walls and pierce multiple enemies, this weapon is superb for use in Caves, homes, or the very dungeons it's found in.

The water bolt gives off light as it moves, from its center and from magic water droplets it sheds. This allows you to find nearby open spaces without blindly digging (as seen in the picture below).

Tips
A good way to use this against a boss is to build a very large closed corridor of any material and lure the boss into it, then letting multiple Water Bolts bounce around.

Water Bolt cannot be used to cool lava for obsidian.

An easy way to find a Water Bolt is to mouse over the books in the dungeon. When you find one, the icon for the Water Bolt will appear by your mouse. You can right click it to pick it up, you don't have to use a hammer. Careful, range is limited (about mining distance with a Pickaxe).