The Fountain stands on the grounds of the Royal Palace in the Emerald City. Clear, sparkling water bubbles up in its golden basin, but it bears a sign that reads, "All Persons are Forbidden to Drink at this Fountain."
Centuries ago, a wicked king ruled the Land of Oz and made himself and his people miserable and unhappy. Glinda placed the Fountain in its present location, and the king drank from its water. His people still feared him, so he made them drink from the fountain as well. Then the king and his people grew wise together. That king placed the warning sign on the Fountain to prevent anyone from drinking of it by accident.
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 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."