As I read in my textbook, aquaporins exclude $H^+$ when absorbing water, but where does this $H^+$ come from? Additionally, is $H_3O^+$ a liquid that looks like regular water?
closed as off-topic by canadianer, AliceD♦ Oct 11 '17 at 10:32
This question appears to be off-topic. The users who voted to close gave this specific reason:
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It doesn't matter where the $H^+$ comes from in the context of this information. The textbook is just saying that the aquaporin is permeable to $H_2O$ but not to $H_3O^+$ (nor, presumably, to $OH^-$).
In any aqueous solution, especially in the presence of acids, some of the molecules will be $H_3O^+$. The pH tells you how many. It doesn't really make sense to think about what a solution of $H_3O^+$ would look like.