Aim The basolateral chloride channel ClC‐Kb facilitates Cl reabsorption in the distal nephron of the human kidney. Functional mutations in CLCNKB are associated with Bartter's syndrome type 3, a hereditary salt‐losing nephropathy. To address the function of ClC‐K2 in vivo, we generated ClC‐K2‐deficient mice. Methods ClC‐K2‐deficient mice were generated using TALEN technology. Results ClC‐K2‐deficient mice were viable and born in a Mendelian ratio. ClC‐K2−/− mice showed no gross anatomical abnormalities, but they were growth retarded. The 24‐h urine volume was increased in ClC‐K2−/− mice (4.4 ± 0.6 compared with 0.9 ± 0.2 mL per 24 h in wild‐type littermates; P = 0.001). Accordingly, ambient urine osmolarity was markedly reduced (590 ± 39 vs. 2216 ± 132 mosmol L−1 in wild types; P < 0.0001). During water restriction (24 h), urinary osmolarity increased to 1633 ± 153 and 3769 ± 129 mosmol L−1 in ClC‐K2−/− and wild‐type mice (n = 12; P < 0.0001), accompanied by a loss of body weight of 12 ± 0.4 and 8 ± 0.2% respectively (P < 0.0001). ClC‐K2−/− mice showed an increased renal sodium excretion and compromised salt conservation during a salt‐restricted diet. The salt‐losing phenotype of ClC‐K2−/− mice was associated with a reduced plasma volume, hypotension, a slightly reduced glomerular filtration rate, an increased renal prostaglandin E2 generation and a massively stimulated renin–angiotensin system. Clckb−/− mice showed a reduced sensitivity to furosemide and were completely resistant to thiazides. Conclusion Loss of ClC‐K2 compromises TAL function and abolishes salt reabsorption in the distal convoluted tubule. Our data suggest that ClC‐K2 is crucial for renal salt reabsorption and concentrating ability. ClC‐K2‐deficient mice in most aspects mimic patients with Bartter's syndrome type 3.