What substance does a salinity indicator measure in the water?

A salinity indicator is specifically designed to measure the concentration of salt in the water, which is typically represented as the total dissolved solids or the salinity levels. Salinity refers to the amount of salt dissolved in water, and it is a critical factor in aquatic environments as it affects the density of the water, the types of organisms that can thrive, and various chemical processes. While chlorine, nitrogen, and fluoride are important substances in water quality and treatment, they do not directly relate to the measurement of salinity. Therefore, identifying salt as the substance measured by a salinity indicator underscores the tool's purpose in assessing the salinity levels essential for understanding aquatic ecosystems and conducting water quality assessments.