Bowl of Commanding Water Elementals
Source: Dungeon Master's Guide
Wondrous item, rare
While this bowl is filled with water, you can use an action to speak the bowl's command word and summon a water elemental, as if you had cast the Conjure Elemental spell. The bowl can't be used this way again until the next dawn.
The bowl is about 1 foot in diameter and half as deep. It weighs 3 pounds and holds about 3 gallons.