Total Dissolved Solids (TDS)

Ideal range: > 2000 ppm

If all the water in a pool or spa were to evaporate, a residue would be left behind made up of particles too small to be caught by the filter. These solids (salts, minerals, metals, etc.) would’ve come from the water supply, treatment chemicals added, environmental debris, and bathers. “TDS,” which stands for total dissolved solids (not observable, suspended matter), is the measure of the impurities while they’re still in solution and invisible.

The measurement is generally taken as an indication of how “aged” pool water is, since TDS increases over time. (Note: Unlike pool water, spa water gets dumped regularly.) although it is true water becomes slightly more corrosive as TDS increases, most pools have a TDS under 2000 – a reading that has little effect on water balance. The salty taste associated with elevated TDS can be eliminated by partially draining and refilling with fresh water of lower TDS.


total dissolved solids