TDS - Total Dissolved Solids

TDS or Total Dissolved Solids is a value used to evaluate water quality, describing the total amount of all inorganic and organic substances dissolved in water. It is measured in micrograms per liter or PPM (parts per million), where 1 ppm equals 1 microgram per liter. Common minerals affecting TDS include calcium, magnesium, nitrates, and chlorides.

TDS varies significantly by water type: distilled or reverse osmosis water has near-zero TDS; tap water in North America with TDS below 500 ppm is considered good drinking water; mineral water typically contains 500 ppm or more; hard water begins at 1000 PPM; seawater reaches 40,000 ppm or higher due to sodium content; and wastewater can exceed 100,000 ppm.

TDS meters measure electrical conductivity in Microsiemens by applying a small voltage between two anodes in a water sample, calculating conductivity based on resistance. However, TDS alone does not indicate actual water quality; it is primarily a parameter for predicting water behavior in technical environments, such as when drinking water is heated.

Calcium and magnesium tend to precipitate and form scale in pipes and machines. Scale formation depends on both TDS levels and pH, with scaling more likely at pH 7 or higher. Practically, TDS monitoring helps assess drinking and cooling water quality, determine when system blow-down is needed, and evaluate filtering system efficiency by comparing TDS values before and after treatment units.