Most of you probably already know this:
Endless Decanter of Water
To obtain, throw a full water pitcher at a water elemental (non summoned) there is a slight chance the elemental will throw back to the player a Endless Decanter of Water. The Decanter can then be linked to a water trough, as long as the player is within 5 tiles outside of a house or anywhere inside a house the Decanter will continuously refill itself.