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Yay, another one. Antonio, the C here is like "from".

Well, maybe I'm too picky but I don't think the translation is correct.

Well, yes, I think so.

Also: Our family needs three gallons of water per day = Нашей семье нужно 12 литров воды в/на день (either one is possible).

ADDED:
It's like the basic option is a "В"...

На.
На каждую семью, на каждого человека.

But:
We sell three thousand cars per day = Мы продаем три тысячи машин в день.