SilverGen PPM and water tester. If you want to test your water for usability prior to making colloidal silver, this is the unit for you. It will read microsiemens (uS/cm) which... to parts per million (PPM) of ionic/colloidal silver after you have produced it.If the water was pure to start with, this meter will read colloidal silver directly in ppm by applying... a correction factor. We have tested our colloidal silver for ppm using the atomic absorption method and this meter reads those samples within a close percent of the laboratory...