Humidify is a Lunar spell that fills all water-carrying vessels in the player's inventory with a single cast. Vessels that can be filled or watered include buckets, fishbowls, jugs, watering cans, tree saplings, bowls, vials, and even clay. Experience gained per cast is always 65, regardless of the number of items watered.

A Magic level of 68 is required to cast this spell, giving 65 experience. It requires 1 Astral rune, 1 Fire rune, and 3 Water runes to cast.