Bowl of Water Elemental Control is needed in the quest of Tenya, a worshipper of the deity Umberlee in the area Area North of the Friendly Arm. It was stolen by worshipper of Talos. It needs to be returned to her, but returning it only earns a favor of the worshippers of Umberlee. This favor can be used in the quest related in the Water Temple in Baldur's Gate.
This magical bowl holds great power in that it grants the owner a certain degree of control over magical creatures known as water elementals. As is the case with all elemental forces, this control can be turned towards either good or evil, law or chaos. One would therefore be well advised to use discretion when dealing with any such creatures.