Clarification of the water-induced structural transitions and electron transfer between ionic liquids (ILs) and a solid surface allows for establishing a unified view of the electrical properties of interfacial ILs via a hitherto unexplored pathway. Here, we propose a simple and effective method to quantitatively identify and extract the transferred electrons between ILs and a solid surface, while demonstrating the critical structural transition of interfacial ILs from ordered stripe structures to disordered aggregation structures. The formation of hydrated anions, rooted in the hydrogen bonds of O-H···O between the anion and water, lies at the tipping point where electron transfer ends and aggregation structure begins. In addition, it is discovered to what extent the hydrophilicity of substrates can affect electron transfer, and a regulation method based on the electric field is explored. These experimental findings may refresh our knowledge of interfacial ILs and provide an effective method for evaluating the intrinsic electrical features of the ILs-solid surface.