Gregory Maguire seems to have wanted to explore the nature of wickedness. So he wrote Wicked: the Life and Times of the Wicked Witch of the West. Contemplating the project I thought Maguire would use his novel to explain how the witch became wicked and, incidentally, explain other things, like why a pail of water melted her.
But it turns out Elphaba (the name Maguire gives "the Wicked Witch of the West", basing it on the initials of the author of the Wizard of Oz) is neither wicked nor a witch nor from the Winkie Country (Oz's western province). She did some things that could be construed as bad -- sicced a swarm of bees on a man, killing him (but the command seems to have been unconscious -- the bees did her will without her realizing it) and she neglected her child (she treats him like a stranger). Though, oddly, she seems to have been born with some evilesque characteristics -- like sharp teeth that make breastfeeding hazardous for Mom. She never studies witchcraft (though her sister, the WWotE, does) but powers seem to manifest nevertheless -- as when she races across a river to rescue a monkey and the river freezes under her feet, saving her from dampness -- but maybe this was coincidence, as even the text suggests, since if a river can freeze instantly why not a pathetic little pail of water? But, and this left me most dissatisfied, what was the basis of Elphaba's allergy to water? No explanation is ever offered -- other than it being inherent, I guess.
At least L. Frank Baum gives us this: "Once the Witch struck Toto a blow with her umbrella and the brave little dog flew at her and bit her leg in return. The Witch did not bleed where she was bitten, for she was so wicked that the blood in her had dried up many years before." One may decide that her dryness had become essential to her in some way. Thus the deadliness of a spot of water.
Though born in the Munchkin Country Elphaba ends up in the Winkie Country because that's where the father of her child lived. Elphaba is seeking forgiveness from her dead lover's widow (forgiveness for having seduced the husband). The widow seems uninclined to give it mainly because it's boring and lonely in Winkieland and if she forgives Elphaba the woman will go away and make Winkieland more boring & lonely than ever.
While Maguire's prose can be well-wrought the text is frequently grim. This is an Oz with a fascist ruler (the Wizard tortures people, has secret police); famine stalks the land; the weather kinda sucks; and amoral capitalists engage Elphaba in tiresome arguments about the nature of evil.