Yes, I agree that of course there are other factors that affect kidney health, metals etc. Sure we should drink clean water and previously I would have agreed with you that about 4 liters is a good amount, but now I have realized that drinking this much water has actually been stopping my kidneys from being able to do what they are supposed to do. It is these broad generalizations that we need to get away from. The fact is everyone will need a different amount of water and this can easily be followed by drinking when we are thirsty and no one will ever convince me otherwise ever again. I would say barely anyone will be actually thirsty for 4 liters of water a day so generally this is probably way too much and will do much more harm than good.