Total dissolved solids (TDS) is a measure of the combined content of all dissolved inorganic and organic substances in water, including minerals, salts, and metals. It is a general indicator of water quality.
Total dissolved solids (TDS) quantifies the total concentration of all dissolved substances in water, including minerals (calcium, magnesium, sodium, potassium), salts (chlorides, sulfates, bicarbonates), metals, and organic matter that pass through a 2-micrometer or smaller filter. TDS is determined either gravimetrically by evaporating a filtered sample and weighing the residue, or estimated from electrical conductivity measurements using a conversion factor typically between 0.5 and 0.9. The EPA has established a secondary (non-enforceable) drinking water standard of 500 mg/L for TDS, above which water may have an objectionable taste, odor, or color and may cause staining. Natural TDS levels vary widely based on geology, with groundwater from limestone aquifers typically having higher TDS than surface water from granitic watersheds. Irrigation water with TDS above 2,000 mg/L can cause salinity problems in agricultural soils. TDS is also important in aquaculture, industrial process water, and aquifer characterization. Reverse osmosis and distillation are the primary treatment methods for reducing TDS in drinking water.