What Are Total Dissolved Solids?

What is TDS?
August 6, 2017
Where Do Dissolved Solids Come From?
August 6, 2017

What Are Total Dissolved Solids?

  • “Dissolved solids” refer to any minerals, salts, metals, cat ions or anions dissolved in water. This includes anything present in water other than the pure water (H20) molecule and suspended solids. (Suspended solids are any particles/substances that are neither dissolved nor settled in the water, such as wood pulp.)
  • In general, the total dissolved solids concentration is the sum of the cat ions (positively charged) and anions (negatively charged) ions in the water.
  • Parts per Million (ppm) is the weight-to-weight ratio of any ion to water.
  • A TDS meter is based on the electrical conductivity (EC) of water. Pure H20 has virtually zero conductivity. Conductivity is usually about 100 times the total cat ions or anions expressed as equivalents. TDS is calculated by converting the EC by a factor of 0.5 to 1.0 times the EC, depending upon the levels. Typically, the higher the level of EC, the higher the conversion factor to determine the TDS. NOTE – While a TDS meter is based on conductivity, TDS and conductivity are not the same thing. For more information on this topic, please see our FAQ page.

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