The Forbidden Fountain is the "most dangerous" source of magical influence in Oz. Its Water of Oblivion produces amnesia in any and all who drink it.
Artists have usually depicted the Fountain as a round basin with spouts of water shooting up in its center.
When Ozma first tells Dorothy and others about the Fountain, she states that Glinda "placed" the Fountain in its present location, where it has been for "centuries." Ozma uses the Water of Oblivion to defeat the invasion of the Nomes, Phanfasms, Whimsies, and Growleywogs. (The Emerald City of Oz)
Some later Oz writers have found the Fountain irresistibly tempting. It is the crucial element in the McGraws' The Forbidden Fountain of Oz. It also plays important roles in Jack Snow's The Shaggy Man of Oz, Rachel Cosgrove Payes's The Wicked Witch of Oz, and Edward Einhorn's Paradox in Oz.
In creating the Forbidden Fountain, L. Frank Baum drew, perhaps unwittingly, on a rich store of folklore and legend. The idea of the drink that purges the drinker's memories can by found in Norse and Hindu and other world mythologies. In the West, it is most familiar in the water of Lethe in Greek mythology: the souls of the recently dead drink from the river Lethe to forget their old lives.
Baum is perhaps unusual in the stress he places on the moral influence of the Water of Oblivion. In his works, the drink not only wipes the memory but leaves the drinkers "as innocent as babes."