Illinois Water Supply Planning




Total dissolved solids (TDS):
     The total amount of solids remaining when a water sample is evaporated to dryness, in mg/L. In principle, it is the sum of all dissolved constituents, with bicarbonate converted to equivalent carbonate. Dissolved is operationally defined as all molecules not filtered out by a 0.45 um filter. Fresh waters are defined as having TDS < 1000 mg/L, with the secondary standard for drinking water being 500 mg/L. Brackish waters are defined as having TDS from 1000 20,000 mg/L, generally considered too saline to be potable (without treatment). Saline waters have similar or greater TDS than seawater (35,000 mg/L). Brines are waters significantly more saline than seawater (TDS > 100,000 mg/L).

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