Do higher levels of fluid intake really help the kidneys?

Summary: higher levels of fluid intake do protect against chronic kidney disease.Chronic kidney disease (CKD) is far more common than generally known. Drinking water in excess of that demanded by thirst has been criticized as a useless effort lacking in benefit. However, a paper published in the journal Nephrology presents evidence that relatively high levels of fluid intake, up to 3.2 liters per day, does in fact protect against chronic kidney disease (CKD). The authors...

"...evaluated the association between fluid and nutrient intake and chronic kidney disease (CKD)."

They gathered data from two studies, calculating intakes of over 40 nutrients, total daily energy intake, and the total content of fluid and drinks, which they correlated to CKD as the primary outcome. What did the data show?

"Participants who had the highest quintile of fluid intake (3.2 L/day) had a significantly lower risk of CKD. These findings were consistent across both study periods, both equations to calculate GFR and both GFR thresholds."

Increasing fluid intake beyond the amount compelled by thirst has been criticized as mythic folk medicine with no science to justify the practice. The evidence presented in this study suggests that the widespread scourge of chronic kidney disease can be reduced by higher levels of fluid intake. The authors conclude:

"Higher intakes of fluid appear to protect against CKD. CKD may be preventable at a population level with low-cost increased fluid intake."

3.2 liters is 13.5 cups, a lot of water. It remains to be proven, but I suspect that somewhat lesser amounts also have benefit.