One of the long term side effects of Prograf (tacrolimus) is that it can cause scarring of the kidney. This does not always happen but it is a known adverse effect or side effect in a limited number of transplant recipients. The drug is the best one we have for keeping transplanted organs from being rejected but it also has this long term effect in some individuals that is very unfortunate. I don’t think that drinking a large amount of water will help. Once this kidney toxicity occurs, the best we can do is try to make the kidney last as long as it can. In some cases, other drugs can be substituted for Prograf, but none are approved for liver transplantation. If the kidney continues to fail, then you may have to go back on the transplant list and get a second kidney. As long as your liver is still working, you can have dialysis and hopefully get re-transplanted in the future.
Unfortunately, all transplant drugs have desirable and undesirable effects and we must use them to the best of our abilities.