Kalim describes his unique magic Oasis Maker (hidden meaning: The Enduring Blessing) as the ability “to expend a little bit of magic power to produce large volumes of the finest water.”
Kalim: “The best way I can describe my signature spell, Oasis Maker, is it makes really good water, and a lot of it.”
When Grim points out that “there are plenty of other spells that let you conjure water…” Kalim says, “The point of Oasis Maker is its efficiency. It produces a lot using a very small amount of magic. Back before the advent of running water, one would have had to draw their own water and boil it to sterilize it. A spell like mine would have been a tremendous boon back then.”
He then seems to come over to Grim’s way of thinking, saying, “But I guess you’re right. Now that running water is a widespread service, it’s not the most useful of spells. But hey! I’m still confident that the water I conjure is the finest, most delicious water in all the land.”
Kalim later downplays his unique magic to Azul, saying, “It’s pretty useless when we’ve already got running water,” but Azul disagrees: “Some countries don’t HAVE that sort of infrastructure. Your power would make you nothing short of a hero to those people!”
Jamil also seems to undervalue Kalim’s unique magic, calling it a “little trick” that he had written off “as a worthless spell only good for watering plants or filling a pool.” Azul says that Jamil does not appreciate his power for what it is.
The examples we have seen of Oasis Maker thus far involve Kalim filling an oasis, restoring a dry river and “manipulating” a fountain during his dorm vignette.
Kalim fills up a pail with water in the school library in order to wash gym clothes, explaining that he is capable of adjusting the amount of water that he produces:
My signature spell lets me produce large volumes of water for a small amount of magic.
Conversely, that means even a teensy amount of magic generates a whole bunch of water, so it’s hard to fine-tune it. But I’ve managed to fill one cup without overflowing it before…
In Book 7 Kalim uses his unique magic twice more, once to cool people down and again so that people will have something to drink.
Twisted Wonderland Reference Note 