Hi David. I am not in the mood to get into this in detail but all you need do is a google search to learn that there is plenty of evidence that the 8X8 water rule is very questionable. The origins of the ‘rule’ are not clear but it has been suggested in many places over the years that bottled water companies at very least promoted it.
Your status as a ‘renal patient’ gives you a unique view of kidney health but may not be applicable to the average low carber/keto’er. The current evidence now points to insulin playing a role in kidney disease as well as gout (uric acid build up). I think most people will not experience kidney disease (stones included) if they follow a diet that keeps insulin low.
I pointed to my own experience because I am 63 yrs. old and during this past 10 yrs. have been strictly keto and have another 3 or so years of low carb prior. My PCP has been openly pleased with my kidney function (among lots of other health markers).
My reverse experience is that my beloved Mother had kidney failure as part of the multiple conditions of type 2 diabetes. I am sure that in her case, drinking 8x8 would not have made a single bit of difference for her. A low carb diet on the other hand, may have made all the difference but that was not in the advice of the professionals at the time.
I guess my message is that there is evidence for anything and everything a person may want to confirm for themselves so read both sides and learn to think critically and then come to your own decisions. I think this forum has plenty of folks that have come to that same conclusions and why it is such an interesting and good place to be!!!