What does the TDS meter measure?

The TDS (Total Dissolved Solids) meter is designed to measure the concentration of dissolved solids in water, which includes various ions such as salts, minerals, and metals. When a TDS meter is used, it essentially provides a numerical value that represents the sum of all these dissolved substances in the water, giving an overall indication of its quality and purity.

Measuring dissolved solids is important for various applications, such as water treatment and environmental monitoring, as a higher concentration of TDS can affect the taste and safety of drinking water, as well as the efficiency of the water treatment process. This is why the correct answer focuses on the sum of all ions in the water, which is the primary function of a TDS meter.