Water to Dust

Pick a location within range. All water in a 30ft cube surrounding that point is turned to dust. Any creature within that area when the spell is cast must make a Con save against your spell save DC, taking 4d8+20 Poison damage on a fail, which bypasses immunities and resistances as part of the water in their bodies is turned to fine dust, or simply gets buried under dust on a success, provided they were under water beforehand. 

The location the spell takes effect at becomes difficult terrain, as the dust is very fine and uncompressed, and any creatures killed by this spell become dried husks vaguely resembling what they were in life.