In the present study, Cu-based nanomaterials are synthesized by initiating spark discharges between two copper electrodes immersed in de-ionized water. The electrical conductivity of water is varied by adding HCl at very low concentrations. The discharge and water properties are determined by measuring the current-voltage waveforms and monitoring water acidity and conductivity, respectively. Scanning electron and transmission electron microscopy analyses of the produced nanoparticles show that increasing water conductivity, by adding HCl, promotes the synthesis of Cu-based nanomaterials. Depending on the initial water conductivity, various nanostructures are observed, including nanoflakes of cuprite (Cu2O), dendrites with high Cu content, and unordered micrometric aggregates with a mixed Cu/Cu2O content. The initial water conductivity also affects the chemical structure, mainly the relative Cu/Cu2O crystalline content.