Ramiel, after spending a bit more time with the dust, it finally clicks. This is the driest dust he has ever felt, so dry it feels like it saps the moisture out of his hands and immediate surrounding air. Unrelated to the dust, you get an odd sensation coming from the northern tunnel.
OOC:
Dust of Dryness: This small packet contains 8 pinches of dust. You can use an action to sprinkle a pinch of it over water. The dust turns a cube of water 15 feet on a side into one marble-sized pellet, which floats or rests near where the dust was sprinkled. The pellet's weight is negligible. Someone can use an action to smash the pellet against a hard surface, causing the pellet to shatter and release the water the dust absorbed. Doing so ends that pellet's magic.
An elemental composed mostly of water that is exposed to a pinch of the dust must make a DC 13 Constitution saving throw, taking 10d6 necrotic damage on a failed save, or half as much damage on a successful one.