Solids in water refer to suspended or dissolved materials in drinking, surface and brackish waters, as well as domestic and industrial wastewaters. Solids may affect water and wastewater quality in a number of ways. Waters with high dissolved solids are generally of lower quality and may cause adverse physiological responses in the consumer, so a maximum of 500 mg of solids per liter is desirable for drinking water.

TDS stands for total dissolved solids, which is the sum of the concentrations of all ions in water. Dissolved substances in water may be “organic” or “inorganic” in nature. Total dissolved solids (TDS) cannot be considered the main criterion for determining water quality and is more a measure of the degree of clarity of water.