What is tds (total dissolved solids)?
TDS is the total mass of dissolved minerals, salts and metals in water, in parts per million. In cleaning it governs whether a rinse dries spot-free; in cooling systems it drives scaling risk and sets how much blowdown a tower needs.
TDS is usually estimated from conductivity rather than measured gravimetrically, because the two correlate closely enough for process control and conductivity takes seconds to read.
On a rinse line, TDS is what gets left behind when a droplet evaporates. High-TDS rinse water spots parts no matter how good the cleaner was, which is why cosmetic and precision work specifies a DI final rinse.
On a cooling tower, TDS rising toward the scaling limit is the signal that blowdown is insufficient — the tower is concentrating faster than it is being purged.
