Fountain
Version 0.14: This article may not be up to date for the latest stable release of Crawl.
Fountains are a Dungeon feature often found near shops, altars, and some vaults. They are almost entirely cosmetic, though they do count as shallow water tiles and thus may be used to fuel the Summon Elemental spell, and may contain aquatic monsters, though they are too shallow to cause merfolk characters to transform.
List of Fountains
History
Prior to 0.14, you could quaff from fountains for various effects.
Prior to 0.12, fountains dried by the player would eventually flow again given enough time (1% chance every 20 turns), becoming whatever kind of fountain they were beforehand.