What are Total Dissolved Solids (TDS)?
Total Dissolved Solids (SDT, or TDS for its acronym in English: Total Dissolved Solids) are the number of milligrams of the residue that remains after evaporating a water sample previously filtered through a glass fiber filter with a 1.5 micron opening. The water evaporates and the residue is brought up to 180 ° C. The result is reported in mg / L.
TDS include salts, minerals, metals, and any other organic or inorganic compound less than 1.5 microns or that dissolves in water.
Sometimes TDS are confused with Total Solids (TS), which is the residue that remains after evaporating the same water sample but without filtering.
Total Suspended Solids (SST) are those remaining in the 1.5 micron aperture fiberglass filter. Therefore, STs are the sum of SSTs and SDTs.
The reduction of TDS is achieved through processes such as reverse osmosis, electrodeionization, demineralization or distillation.
What is the most common way to measure them?
The TDS content of a water can be estimated by measuring its electrical conductivity (EC), since those solids that ionize increase the EC. Pure water has an EC of practically zero. There are teams that, through the CE, estimate the TDS, but it must be taken into account that they do not consider those solids that do not ionize when dissolved in water. The value of the TDS in mg / L is between 0.5 and 1.0 times the EC value in micro Siemens / cm (depending on the temperature and the concentration level of TDS).
John DeZuane, Handbook of Drinking Water Quality, 2nd Ed., John Wiley and Sons Inc., New York, 1997.
Frank N. Kemmer, John McCallion, Manual of water, Its nature, treatment and applications Volume I, 1st Ed., McGraw Hill, Mexico, 1988.
EW Rice, RB Baird, AD Eaton, Stanard Methods for the examination of water and wastewater, 23rd Ed., AWWA, USA, 2017.