@Shock,

I don't know for sure why they need all that water, but if they are tempering a Zanpakutou, and if the size of the Zanpakuto of a Captain class Shinigami is as big as Skyscrapers, then, they be needing A WHOLE BUNCH of HOT SPIRIT STEEL, for Ichigo's Gigantonoumous Zanpakutou, YES?