When the Zoras domain was frozen, lake hylia was empty, also the fact of rivers from the domain go to hylia, and the zoras domain has water falls. Assuming this Hyrule is like Oot then zoras domain is presumably the water source, unless it comes from Terminus. (I wouldn't know I didn't play mojoras mask)

Edit: [hider=I figure this is abit appropriate] [img=http://fc08.deviantart.net/fs71/f/2013/133/b/e/be4a45f7d433b6569ab2bc119bd6a660-d4p2io9.jpg] [/hider]