You do one of the following:
Create Water. You create up to 10 gallons of clean water within range in an open container. Alternatively, the water falls as rain in a 30-foot Cube within range, extinguishing exposed flames there.
Destroy Water. You destroy up to 10 gallons of water in an open container within range. Alternatively, you destroy fog in a 30-foot Cube within range.
Using a Higher-Level Spell Slot. You create or destroy 10 additional gallons of water, or the size of the Cube increases by 5 feet, for each spell slot level above 1.