SRD:Dust of Dryness
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Dust of Dryness: This special dust has many uses. If it is thrown into water, a volume of as much as 100 gallons is instantly transformed to nothingness, and the dust becomes a marble-sized pellet, floating or resting where it was thrown. If this pellet is hurled down, it breaks and releases the same volume of water. The dust affects only water (fresh, salt, alkaline), not other liquids.
If the dust is employed against an elemental with the water subtype, the creature must make a DC 18 Fortitude save or be destroyed. The dust deals 5d6 points of damage to the creature even if its saving throw succeeds.