Mel,
As you have observed, hydration in extremely important. Cisplatin is a very harsh chemical on the kidneys. When Cynthia was undergoing chemotherapy at MA General, I remember one doctor telling a patient how important hydration was when working with this chemical. The balance between allowing the drug to work, but not damaging the kidneys is delicate.
Another item to consider is hydration during chemotherapy. Cynthia would consume a large amount of water during each treatment and the technician would always encourage this practice. It would reduce the treatment time because less additional IV hydration was required. Remember, they are monitoring output which is a function of input; either oral or IV.
Let's hope that your dad continues to make good progress during his treatment. Please keep us posted on his progress.
Ed K.