What is the TDS reading of the purified water?
A TDS meter measures only Total Dissolved Solids or minerals; dissolved solids are simply dissolved minerals in an ionic form. A TDS meter does not measure the amount of biological and chemical contaminates. Black Berkey™ elements are designed to leave the healthful and beneficial minerals in your water and to extract only the unwanted heavy metals such as lead and mercury as well as sedimentary minerals such as iron oxide and aluminum. Therefore, your TDS reading will not change much unless you have a significant amount of heavy metals or sedimentary minerals in your water.