This study was conducted to investigate the effect on copper corrosion of adding six different mixtures of orthophosphate and polyphosphate (sodium hexmetaphosphate) to the drinking water. A no-treatment option was also studied. Using a pilot-scale flow-through apparatus containing new copper pipes, studies were performed on site at two small Nebraska public water supplies; both water supplies currently do not treat their water, which comes from deep groundwater wells. At the end of each study, the copper pipes were removed and the pipe scale was analyzed using a Scanning Electron Microscope (SEM). It was found that in all cases orthophosphate reduced copper corrosion and ortho/polyphosphate blends tended to increase copper corrosion. For all pipes fed phosphate inhibitors, their surfaces appeared brown and shiny and no phosphates were found on the surfaces. CuO or/and Cu₂O existed on the surfaces. Includes 19 references, tables, figures.