The new microporous cobalt triazolyl phosphonate MOF 3α[Co4L3(μ3-OH)(H2O)3](SO4)0.5·xH2O (L2- = 4-(4H-1,2,4-triazol-4-yl)-phenyl phosphonate) exhibits exciting features including high water stability, reversible hydration-dehydration, steep water uptake in repeated cycles at low water vapor pressures and reactivation at room temperature under mild evacuation.