TDS vs Hardness vs Conductivity

TDS is the measure of total dissolved solids in fresh water sources. It includes inorganics and organics that typically can pass through a 2 micron filter. Measurement occurs in reality via conductivity. Cations and anions emit charges and are a source of this “conductivity”. There are benchtop meters as well as portable field versions of these meters on the market. For your convenience, all of our TDS solutions are listed here.

Conductivity refers to the electrical conductivity a solution exhibits. Typically, the preferred source is KCl and not NaCl. The units are expressed as micro Mho’s/cm or micro Seimens/cm (Seimens unit was the convention in Europe, mho’s in the US in the past).The opposite of conductivity is resistivity, and its unit is microohms/cm. One can calculate one or the other by having just one specification and calculating the reciprocal value. Resistivity is commonly used in water purification systems.

Hardness refers to the amount of calcium and magnesium in water. A hardness solution will have a conductivity value, a separate hardness value expressed in equivalent CaCO3 units, and a TDS value in ppm. But the opposite is not necessarily true. You can have conductivity and TDS values and NOT a hardness value if no Ca or Mg ions are present. Exaxol offers standards for Conductivity, both conductivity combined with TDS, and water standards for drinking water/wastewater for hardness as well.

Exaxol is enhancing its current offering of conductivity standards to include a TDS (total dissolved solids) value right on the label for the user’s convenience. The tolerance for a standard is a realistic and competitive 0.5%. The TDS values will be based on KCl.

Now, an analyst will be able to change modality on a meter without necessarily having to change the standard. For TDS standards not listed on our website just ask one of our customer service representatives for availability by calling (727) 524 – 7732.