This large container is usually fashioned from blue or green semi-precious stone (malachite or lapis lazuli, for example, or sometimes jade). It is about one foot in diameter, half that deep, and relatively fragile. When the bowl is filled with fresh or salt water, and certain words are spoken, a water elemental of 12 Hit Dice will appear. The summoning words require one round to speak.
Note that if salt water is used, the elemental will be stronger (+2 hp per Hit Die, maximum 8 hp per die, however). Information about water elementals can be found in the Monstrous Compendium. (See also bowl of watery death.)
In Ravenloft: An elemental cannot return to its native plane unless it finds a normal escape route from Ravenloft. If an elemental is freed somehow from control, it attacks the character who summoned it.