Kidney function is most often estimated indirectly, based on measurements of the amount of a chemical called creatine in the blood. Higher functioning kidneys lower creatine levels more effectively. But lowering the amount of creatine generated by your diet, by cutting out animal products, will also lower the creatine measured in your blood. That change in measurement does not reflect an actual improvement in your kidney function, I'm sorry to say.
At lower levels of kidney function, attempting to game the numbers in this way, by minimizing the creatinine you consume and by over-consuming water, could be dangerously misleading. And it shouldn't distract from measures that do stop the decline in kidney function, like blood pressure control and avoidance of certain kidney-damaging meds (e.g. high dose ibuprofen).
Good luck!