Digital TDS Meter 4-in-1 Water Quality Tester TDS (Total Dissolved Solids) is a measurement of all solids dissolved in drinking water and is mainly made up of minerals. A high level of TDS is an indicator of potential concerns and should be investigated before drinking. This TDS meter is widely used in all water quality tests. Water Purification Applications, Aquaculture, Hydroponics, Pool & Colloidal Silver, Water Treatment and more. It is a must-have item for the family and is able to test tap water, distilled water, bottled water and more. This 4-in-1 TDS meter combines TDS, EC, and a temperature meter for improved accuracy.