Reticulated vitreous carbon 45 pores per inch is adopted to deposit copper(II) from dilute solutions of 10-20 ppm to below 1 ppm. Three working potential values are tested: E = -0.4 V and E = -0.5 V, at which metal deposition is under diffusion control, and E = -0.25 V, at which the effect of O-2 reduction is limited, but deposition does not occur at its maximum rate. A theoretical model, which takes into account the reabsorption of O-2 from air, is proposed to interpret the trend of faradic yield as the metal concentration in the solution becomes lower. The behavior of the system is correctly interpreted from the model when electrolyses are performed at E = -0.4 V.