Check valves, which utilize diaphragms to filter impurities while separating purified water from wastewater, from Minneapolis-based Minnesota Rubber/QMR Plastics, are molded to tight dimensions of thermoplastic urethane. Replacing fabric reinforced rubber diaphragms, the TPU diaphragms improve product performance. The water purification device is part of an under-the-sink drinking system. The check valves are critical to the system’s quality and must perform without leakage.