The trace toxic metal copper was assayed using mercury immobilized on a carbon nanotube electrode (MCW), with a graphite counter and a reference electrode. In this study, a macro-scale convection motor was interfaced with a MCW three-electrode system, in which a handmade MCW was optimized using cyclic- and square-wave stripping voltammetry. An analytical electrolyte for tap water was used instead of an expensive acid or base ionic solution. Under these conditions, optimum parameters were 0.09 V amplitude, 40 Hz frequency, 0.01 V incremental potential, and a 60-s accumulation time. A diagnostic working curve was obtained from 50.0 to 350 ${mu}g/L$. At a constant Cu(II) concentration of 10.0 ${mu}g/L$, the statistical relative standard deviation was 1.78% (RSD, n = 15), the analytical accumulation time was only 60 s, and the analytical detection limit approached 4.6 ${mu}g/L$ (signal/noise = 3). The results were applied to non-treated drinking water. The content of the analyzed copper using 9.0 and 4.0 ${mu}g/L$ standards were 8.68 ${mu}g/L$ and 3.96 ${mu}g/L$; statistical values $R^2$ = 0.9987 and $R^2$ = 0.9534, respectively. This method is applicable to biological diagnostics or food surveys.