This paper presents an approach to the simultaneous faults detection, isolation and reconstruction in the hydraulic vertical three-tank system. An observer is designed which contains a corrective term based on a second-order sliding mode control algorithm featuring global convergence properties. Thanks to the proposed global observer, the reconstruction of certain faults and/or disturbances can be performed without requiring any filtration. The effectiveness of the proposed method is shown by means of a simulation example and then validated by performing real experiments.