^ ... Okay, you need to think in more general terms...

The water that we drink on Earth has been everywhere... I mean everywhere. Down the sky, in drains, from contaminated areas, the ocean, behind people's bums and other unpleasant areas etc. And guess what? We still drink it. It's to survive and the cycle starts all over again.

This is the same with Hyrule. The water doesn't have to come all the way from Zora's Domain. It rains in Hyrule and it contributes to a large percentage of the water source.

I'm saying that it doesn't really matter that the water source comes from the King's behind. He is a fish person so he would be a lot cleaner that the average Hylian that would sit there. And hey, Link walks through areas where there are dead people and blood from enemies and his boots are splashing all over the place in Zora's Domain. Now that's contamination...

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