Total Dissolved Solids from Conductivity
TDS (mg/L) = k x EC (uS/cm at 25 C), k commonly 0.55-0.75 (default 0.65). 1000 uS/cm -> 650 mg/L, with a 550-750 band from the k range so it is not read as exact. An estimate, not a gravimetric TDS; calibrate k to a lab result. The operator of record governs.
Formula and source
tds_mgl = k_factor x conductivity_us_cm; k commonly 0.55-0.75 (default 0.65).
Total dissolved solids from electrical conductivity (Standard Methods 2510), by name.
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