Polymeric nickel complexes with salen-type ligands (NiSalen) can serve as useful materials for a range of applications, including sensors, catalytic systems and energy storage devices. Although they surpass convenient conductive polymers in some aspects, they are still in the shadow of them. What pushes researchers away from NiSalen polymers is the low reproducibility of their electrochemical response, which sometimes can vary from day to day. Despite the convenient conductive polymers, which electrochemistry is often tolerant to moisture, most of the NiSalen polymers are highly water sensitive, which causes the uncertainty of their behavior, including the degradation of electrochemical activity and electrical conductance. In the present study, we demonstrate how NiSalen polymers degrade in the presence of H2O, and how the 3-substituent alternates the ultimate site of the H2O attack on the polymer. By a combination of the computational, electrochemical and spectroelectrochemical techniques, we demonstrate that the water-promoted degradation of the NiSalen polymer occurs only while it is oxidized. We have found that H2O attacks the Ni atom of the polymer, switching off charge transport along the polymer chain, but an introduction of CH3O-groups in the ligand structure changes the binding mode of H2O, protecting the polymer from degradation. © 2023 Elsevier B.V.