Which of the following statements is true regarding TSS and TDS?

The statement that TSS (Total Suspended Solids) and TDS (Total Dissolved Solids) combined contribute to total solids is true because both TSS and TDS represent different components of solids in water. TSS refers to solids that are suspended in the water column and can be removed by filtration, while TDS includes all the dissolved substances present in the water. Together, they provide a comprehensive measure of the total solids in a water sample, which is important for assessing water quality and its treatment processes.

Understanding the relationship between TSS and TDS is crucial for water treatment, as both metrics can indicate different aspects of water pollution and help in evaluating the effectiveness of filtration and treatment methods. This makes option C the correct choice, as it highlights the importance of both measurements in the context of total solids.