Optimal daily water intake to prevent chronic kidney disease (CKD) progression is unknown. Taking the kidney’s urine-concentrating ability into account, we studied the relation of kidney outcomes in patients with CKD to total and plain water intake and urine volume.Including 1265 CKD patients [median age 69 years; mean estimated glomerular filtration rate (eGFR) 32 mL/min/1.73 m2] from the Chronic Kidney Disease–Renal Epidemiology and Information Network cohort (2013–19), we assessed fluid intake at baseline interviews, collected 24-h urine volumes and estimated urine osmolarity (eUosm). Using Cox and then linear mixed models, we estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for kidney failure and eGFR decline associated with hydration markers, adjusting for CKD progression risk factors and eUosm.Patients’ median daily intake was 2.0 L [interquartile range (IQR) 1.6–2.6] for total water and 1.5 L (1–1.7) for plain water, median urine volume was 1.9 L/24 h (IQR 1.6–2.4) and mean eUosm was 374 ± 104 mosm/L. Neither total water intake nor urine volume was associated with either kidney outcome. Kidney failure risk increased significantly with decreasing eUosm ˂292 mosm/L. Adjusted HRs (95% CIs) for kidney failure associated with plain water intake were 1.88 (1.02–3.47), 1.59 (1.06–2.38), 1.76 (0.95–3.24) and 1.55 (1.03–2.32) in patients drinking &lt;0.5, 0.5–1.0, 1.5–2.0 and &gt;2.0 L/day compared with those drinking 1.0–1.5  L/day. High plain water intake was also significantly associated with faster eGFR decline.In patients with CKD, the relation between plain water intake and progression to kidney failure appears to be U-shaped. Both low and high intake may not be beneficial in CKD.< Réduire