In the 1939 film "The Wizard of Oz", how is the Wicked Witch of the West killed?

The Wicked Witch of the West in the 1939 film "The Wizard of Oz" is killed when Dorothy throws a bucket of water on her, in attempt to put out a fire the witch bestowed on the Scarecrow. In the novel, Dorothy simply throws it on her in a fit of anger.

The Wicked Witch's most popular depiction comes from the classic 1939 Hollywood musical movie loosely based on Baum's book, "The Wizard of Oz", where she was portrayed by late actress Margaret Hamilton. Hamilton's iconic characterization introduced green boogeyman skin and this has been continued in later literary and dramatic representations of Oz, including Gregory Maguire's highly praised revisionist Oz novel titled "Wicked: The Life and Times of the Wicked Witch of the West".

In Maguire's story the Witch's name is "Elphaba" who is green due to her mother consuming "Green Miracle Elixir" while she was pregnant with her. In the 2013 Oz film by Walt Disney pictures "Oz the Great and Powerful", the pre-Wicked Witch of the West is a young and innocent "Good Witch" named Theodora, who tragically turns green from a green poison apple that causes her heart to shed itself from all its goodness.

Accordingly, when noting her death, experts like to guess that due to the fact the Wicked Witch of the West is so evil, a substance such as water, is simply too pure for her old, bloodless body. The water has to cause her death.