My mistake friend. I misread a certain post and got my information mixed up. To be fair though we are both incorrect. The source of both is in fact, Death Mountain. 
I read that it was a common misconception that zoras domain was the source of water in hyrule and based my information off of that, but upon further study of the text, it was a different lake entirely and not lake Hylia. [url=http://zelda.wikia.com/wiki/Lake_Hylia]