TDS to Conductivity Proxy

Estimate Total Dissolved Solids in real time from a conductivity reading, fast enough for operational control where the gravimetric evaporation test is too slow.

$$\text{TDS (mg/L)}\approx 0.7\times \text{Conductivity (}\mu \text{S/cm)}$$

Variables

Symbol	Meaning	Unit
TDS	Total Dissolved Solids	mg/L
Conductivity	Specific conductance of the water	µS/cm
0.7	Empirical conversion factor (rule of thumb, varies with ion type, concentration, and temperature)	dimensionless

Worked example

A reading of 1,000 µS/cm gives TDS approximately 0.7 times 1,000, which is 700 mg/L.

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Part of The Blueprint of Water