Question  Does drinking more water protect against declining kidney function in patients with chronic kidney disease?

Findings  In this randomized clinical trial that included 631 adult patients with chronic kidney disease, the 1-year decline in estimated glomerular filtration rate did not significantly differ between patients who were coached to drink more water compared with patients who were coached to maintain their usual intake (−2.2 vs −1.9 mL/min per 1.73 m²).

Meaning  Coaching to increase water intake did not significantly slow the decline in kidney function in patients with chronic kidney disease at 1-year follow-up.

Importance  In observational studies, increased water intake is associated with better kidney function.

Objective  To determine the effect of coaching to increase water intake on kidney function in adults with chronic kidney disease.

Design, Setting, and Participants  The CKD WIT (Chronic Kidney Disease Water Intake Trial) randomized clinical trial was conducted in 9 centers in Ontario, Canada, from 2013 until 2017 (last day of follow-up, May 25, 2017). Patients had stage 3 chronic kidney disease (estimated glomerular filtration rate [eGFR] 30-60 mL/min/1.73 m²and microalbuminuria or macroalbuminuria) and a 24-hour urine volume of less than 3.0 L.

Interventions  Patients in the hydration group (n = 316) were coached to drink more water, and those in the control group (n = 315) were coached to maintain usual intake.

Main Outcomes and Measures  The primary outcome was change in kidney function (eGFR from baseline to 12 months). Secondary outcomes included 1-year change in plasma copeptin concentration, creatinine clearance, 24-hour urine albumin, and patient-reported overall quality of health (0 [worst possible] to 10 [best possible]).

Results  Of 631 randomized patients (mean age, 65.0 years; men, 63.4%; mean eGFR, 43 mL/min/1.73 m²; median urine albumin, 123 mg/d), 12 died (hydration group [n = 5]; control group [n = 7]). Among 590 survivors with 1-year follow-up measurements (95% of 619), the mean change in 24-hour urine volume was 0.6 L per day higher in the hydration group (95% CI, 0.5 to 0.7; P < .001). The mean change in eGFR was −2.2 mL/min/1.73 m²in the hydration group and −1.9 mL/min/1.73 m² in the control group (adjusted between-group difference, −0.3 mL/min/1.73 m² [95% CI, −1.8 to 1.2; P = .74]). The mean between-group differences (hydration vs control) in secondary outcomes were as follows: plasma copeptin, −2.2 pmol/L (95% CI, −3.9 to −0.5; P = .01); creatinine clearance, 3.6 mL/min/1.73 m² (95% CI, 0.8 to 6.4; P = .01); urine albumin, 7 mg per day (95% CI, −4 to 51; P = .11); and quality of health, 0.2 points (95% CI, −0.3 to 0.3; P = .22).

Conclusions and Relevance  Among adults with chronic kidney disease, coaching to increase water intake compared with coaching to maintain the same water intake did not significantly slow the decline in kidney function after 1 year. However, the study may have been underpowered to detect a clinically important difference.

JAMA 2018; 319: 1870