Water Stone

The Water Stone is an object that can provide an endless stream of water. In Paper Mario, two Lakitus steal it to increase the Puff-Puff Machine's power. One of them accidentally drops it near Rosie, who claims it as her own. The stone was originally from Lily's pond, which gives her all the water she needs to live. Rosie keeps the stone until Mario can find something more beautiful than it.

Trivia

 * This item may be a reference to the Pokémon games, where they have another item known as the Water Stone as well.