A TDS (Total Dissolved Solids) meter measures the concentration of dissolved solids in water, including minerals, salts, and metals. It is crucial for ensuring water quality in various applications, such as drinking water, aquariums, and hydroponics. High TDS levels can indicate the presence of contaminants, affecting taste and safety. By using a TDS meter, like the HM Digital AquaPro Water Quality Tester, you can monitor and maintain optimal water quality, ensuring safe and healthy water for consumption and usage.