Gentlemen, imagine if you will.
Aqua sits on your lap. Your dick enters her anus, unprotected of course. From there you fill her with your pee, giving her a golden enema. But she holds it in. After finishing your business, maybe you force a plug into her. She still holds, and importantly, purifies your liquid gift.
Then as you go on adventuring, you may get tired and require hydration. You lie down and ask her to squat over you. Releasing the plug from the grips of her anal muscles, you receive pure water, straight from the tap.

You are hydrated once again, and only need to wait for your bladder to feel pressure once more to repeat the cycle.