LaMotte AM-21 Water Pollution Detection Outfit - Manual (Page 46)

Total Dissolved Solids Test
Dissolved solids in a natural water are usually composed of the sulfate,
bicarbonate and chlorides of calcium, magnesium and sodium. The US
Public Health Service recommends that the total solids of a potable water be
limited to 500 ppm, but if such a water is not available a total solids content
of up to 1000 ppm may be permitted. From the standpoint of irrigation of
agricultural crops. total solids of 185 ppm or less would be considered low;
between 175 and 500 medium; 500 to 1500 high; and above 1500 ppm very
high. The term salinity is also used to describe the solids content of irrigation
water. In addition to potable and irrigation uses, a high solids content is
undesirable in most industrial process waters. While sodium-hydrogen zeolite
softening and lime-soda softening may affect a reduction in dissolved solids,
for complete removal, however, it is necessary to employ demineralization or
distillation.
Dissolved solids are determined by electrical conductivity methods; by
weighing the residue after evaporation and by ion exchange methods. A
combination of ion exchange and direct titration is used here to estimate the
solids content of a water.
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