I've been thinking about the downside of fire mastery, that is, the fact that you can drown - Lars noted in chat that this is a fairly big penalty, and I would tend to agree. I do think FM could do with a tweak to make it a bit more balanced.
Rather than giving FM's the ability to purchase water walking, I'd like to suggest that they instead not be blown around in the desert. In this way, they can avoid unpreventable death due to inadvertantly getting thrown into water by the desert twisters, but a malicious player can still banish them onto a twister square, and they can always chance travel through twisters when the water forces them into one to progress through the desert.
So yeah, FM's not getting blown around in the desert - what do you think?