Midrash Rabbah describes how the Jews in Egypt became wealthy through the plague of blood by selling their water to the Egyptians who were desperate. This may be a thought experiment as I haven't seen anywhere else address this matter, but my son asked me whether the Egyptians were able to pay for the water and then provide it to other Egyptians in turn.
This led to a spirited debate at the Shabbos table with all present split evenly with their thoughts on whether or not the Egyptian's purchase was exclusive (i.e. for himself only, or perhaps even for those he had in mind to purchase) or rather once he made the purchase/acquisition it remained water and he could share with anyone he liked.
If anyone has thoughts or better yet sources that deal with this question, I'd be much obliged!
