There are 2 books which I think are nice for a nephro rotation. First is "Renal Pathophysiology-the essentials" by Rose and Rennke (Rose is the UpToDate guy). It's a nice concise text that covers most of the major renal diseases. The other one, which might be hard to get a hold of, is "Manual of Clinical Dialysis" by Suhail Ahmad. It's kinda dry, and can be a bit technical, but since no one really effectively explains how dialysis works in med school, it's good to get the basics of how it works, and to get down the terminology.