Total Dissolved Solids (TDS)

Definition - What does Total Dissolved Solids (TDS) mean?

Total dissolved solids (TDS) are a measure of the collective content of all inorganic and organic substances contained in a liquid. It can be suspended in forms such as:

  • Molecular
  • Ionized
  • Micro-granular (colloidal sol)

The main application of TDS is in the study of water quality for streams/rivers and lakes. It is used as an indication of characteristics of drinking water and as an aggregate indicator of the presence of a broad array of chemical contaminants.

TDS is differentiated from total suspended solids (TSS). TSS cannot pass through a sieve of two micrometers, yet are indefinitely suspended in solution.

Corrosionpedia explains Total Dissolved Solids (TDS)

Total dissolved solids are the amount of organic and inorganic dissolved substances like minerals, metals and salts that may be found in water. It includes everything present in water other than pure H2O and suspended solids. TDS can be from natural sources like dissolved rock, or from man-made chemicals such as volatile organic chemicals (VOCs). In general, the total dissolved solids concentration is the sum of the cation (positively charged) and anion (negatively charged) ions in the water.

Total dissolved solids are measured as parts per million (ppm), and standard drinking water recommends a limit of 500 ppm. The lower the TDS, the better the water quality. For drinking water and fountain beverages, a TDS of up to 500 is acceptable, but for boiler-based steam ovens, TDS should be kept very low—less than 100 ppm.

High TDS levels indicate hard water. This can:

  • Cause scale buildup in pipes, valves and filters
  • Reduce performance
  • Increase system maintenance costs

Typically, in industrial applications, total dissolved solids are tested frequently, and filtration membranes are checked in order to prevent adverse effects. Common water filter and water purification systems include:

  • Carbon filtration
  • Reverse osmosis (RO)
  • Distillation
  • Deionization (DI)

The effectiveness of water purification systems in removing total dissolved solids is diminished over time, so it is highly suggested to monitor the quality of a filter or membrane and replace when required.

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