How can total dissolved solids (TDS) in water supply be accurately measured?

Total dissolved solids (TDS) refers to the concentration of dissolved substances in water, usually expressed in milligrams per liter (mg/L). The most accurate method for measuring TDS involves the process of evaporation. By filtering a measured volume of water to remove suspended solids, the filtered water can then be evaporated, leaving behind the dissolved solids. Weighing the residue left after this evaporation provides a direct measurement of TDS, as it accounts for all dissolved ions and molecules that were present in the original sample.

This method is particularly reliable because it captures all forms of dissolved substances, including salts, minerals, and other organic and inorganic compounds. Other methods might not accurately represent the total concentration of dissolved materials. For instance, simply weighing a measured volume of water does not quantify dissolved solids, as they are not part of the water's weight. Filtering a measured volume and weighing the residue on the filter paper also misses the dissolved substances that pass through the filter. Equating TDS measurement to specific conductance overlooks the need to consider total mass, as specific conductance is influenced by the types and concentrations of ions and does not provide a weight measurement. Therefore, evaporation is the preferred method for accurately determining TDS in water supply.