Tds water quality testing pen drinking water detector tds water tester ppmtds-3 handheld meter with carrying case is a tool to measure total dissolved solids (tds) or the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water. It is very portable, reliable and accurate in testing water and other solutions due to its advanced microprocessor technology. This handheld meter is ideal for all water purification applications, wastewater regulation, aquaculture, hydroponics, and colloidal silver. Perfect for both consumer or commercial use.Tds, which is based on conductivity, is expressed in parts per million (ppm) or milligrams per liter(mg/l). Tds includes any conductive inorganic element present other than the pure water molecules (h2o) and suspended solids.