The electric potential in a nonequilibrium electrolyte solution with a common ion is studied. We have used an observable electric potential (that measured in the metallic phase of an electrode in equilibrium with the solution) instead of the unmeasurable electric potential usually invoked. The phenomenological equations deduced from the dissipation function of irreversible thermodynamics describe the system in a precise, clear, and simple manner when we consider this observable electric potential. An interesting property of this formalism is the distinction between distribution equilibrium and electric equilibrium. The phenomenological coefficients are related to well-known variables such as the specific electric conductance, transference numbers, and diffusion coefficients. The utility of this new formalism is shown by evaluating the profile of the electric potential in a liquid junction.