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TDS and Electrical Conductivity

TDS - Electrical Conductivity (water conductivity)

The table stated below can be used to calculate the TDS (total dissolved solids) as well as the cation and anion composition from a water analysis. Please also use the following website for more information.

value & unit weight charge in mmol/l in mg/l in meq
Cl-
NO2-
NO3-
F-
HCO3-
CO32-
SO42-
H2PO4-
Na+
K+
NH4+
Mg2+
Ca2+
Fe2+
Mn2+
Al3+

TDS in ppm

anion sum
cation sum
Difference between sum of anions and cations: = % total amout of ions
For more than 10% you should check your analysis!

mg/l to ppm to tds to mmol/l to meq to EC to μS (microSiemens)



TDS and electrical conductivity

The term TDS describes all solids (usually mineral salts) that are dissolved in water. The TDS and the electrical conductivity are in a close connection. The more salts are dissolved in the water, the higher is the value of the electric conductivity. The majority of solids, which remain in the water after a sand filter, are dissolved ions. Sodium chloride for example is found in water as Na+ and Cl-. High purity water that contains in the ideal case only H2O without salts or minerals has a very low electrical conductivity. The water temperature affects the electric conductivity so that its value increases from 2 up to 3 % per 1 degree Celsius.

Conversion electrical conductivity into TDS

If your water analysis indicates the TDS and the electrical conductivity, then it should be possible to establish the following relation.

+ 500 ppm correspond to 1000 μS / cm or 1 EC

This can be easily measured with a TDS meter. NPK meters that measure the nitrate-, phosphate- and potassic concentration are often used in the horticulture industry. When using a NPK meter the relation between TDS and electrical changes to the below stated value.

+ 700 ppm correspond to 1000 μS / cm or 1 EC

The EC determination can be done in different ways. One possibility is the usage of an ion specific conductivity coefficient. This coefficient is listed in charts though for their usage it is necessary to have an exact water analysis because every single ion affects the conductivity. An example for such a chart can be found in the „Handbook of Chemistry and physics” 76th edition, S. 5-90“.

Due to the fact that the electrical conductivity measuring depends on the water temperature it is difficult to determine it with an Internet application.

To convert the different conductivity units you can use our conductivity converter.







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