Heck, looking back at it, Foa even says "certainly, the magic she uses is like a miniature version of the actual phenomenon", meaning it isn't even something they don't know, because he's able to confirm that it matches the science. That's even worse than I thought initially, because it's not even that they don't know about the water cycle, but that they do, and nobody thought to ever try to emulate the water cycle with water magic until Aoi said "hey why don't you try to do it with magic" with no further explanation? Really? That just feels ridiculous.