• Jessica M Sontrop, Shi-Han Huang, Amit X Garg, Louise Moist, Andrew A House, Kerri Gallo, and William F Clark.
• Division of Nephrology, Department of Medicine, London Health Sciences Centre, London, Ontario, Canada Department of Epidemiology & Biostatistics, Western University, London, Ontario, Canada.
• BMJ Open. 2015 Nov 24; 5 (11): e008634.

ObjectivesIncreased water intake may have a beneficial effect on the kidney through suppression of plasma vasopressin. We examined the effect of increased water intake on plasma copeptin (a marker of vasopressin) over 6 weeks in patients with chronic kidney disease.DesignSecondary analysis of a randomised controlled parallel-group pilot trial.SettingCanada, 2012-2013.Participants28 patients with stage 3 chronic kidney disease randomised (2:1) to a hydration (n=17) or control group (n=11).InterventionThe hydration group was coached to increase water intake by up to 1.5 L/day for 6 weeks. The control group was asked to maintain regular water intake.Measures And OutcomesParticipants provided blood and 24 h urine samples at baseline and 6 weeks. Change in plasma copeptin was compared within and between study groups.ResultsParticipants were 64% male with a mean age of 62 years and an estimated glomerular filtration rate of 40 mL/min/1.73 m(2). Between baseline and 6 weeks, 24 h urine volume increased by 0.7 L/day in the hydration group, rising from 2.3 to 3.0 L/day (p=0.01), while decreasing by 0.3 L/day among controls, from 2.0 to 1.7 L/day (p=0.07); between-group difference: 0.9 L/day (95% CI 0.37 to 1.46; p=0.002). In the hydration group, median copeptin decreased by 3.6 pmol/L, from 15.0 to 10.8 pmol/L (p=0.005), while remaining stable among controls at 19 pmol/L (p=0.76; p=0.19 for the between-group difference in median change); the between-group difference in mean change was 5.4 pmol/L (95% CI -1.2 to 12.0; p=0.11).ConclusionsAdults with stage 3 chronic kidney disease can be successfully randomised to drink approximately 1 L more per day than controls. This increased water intake caused a significant decrease in plasma copeptin concentration. Our larger 12-month trial will examine whether increased water intake can slow renal decline in patients with chronic kidney disease.Trial Registration NumberNCT01753466.Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

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