How can kidney function be improved for someone with polycystic kidney disease? please suggest something other than improving diet/water/exercise.

Blood pressure : If you have ADPKD then it's generally maintaining a healthy lifestyle but making sure you are treating things that can worsen renal function like high blood pressure. That is probably the most important thing outside of diet (low sodium), exercise, and good hydration. Possibly making sure you don't have high cholesterol could potentially help with renal function.