Determination of Total Dissolved Solids (TDS) in The Water samples


Total Dissolved Solid (TDS) is defined as the substances remaining after evaporation and drying of a water samples. The remaining fraction is approximately equivalent to the total content of the dissolved and suspended matter in the water sample.

Non-filterable residue corresponds to the Total Suspended Solids (TSS) and the filterable residue is the TDS.

Determination of TDS can be used to check the accuracy of analyses when relatively complete analysis has been made on a water sample.

This is accomplished by comparing the value of calculated TDS with the measured value. Ion concentration, in mg/L of constituents, required to calculate the TDS are as follow:

Calculated TDS= 0.6 (alkalinity) =Na+K+Ca+Mg+Cl+SO4+SIO3+ (NO3-N) +F

The measured TDS concentration should be higher than the calculated value, because a significant contributor may not be included in the calculation. If the measured value is less than the calculated value, all values are suspect and probably in error.

If the measured value is higher than the calculated value, the low ion sum is suspect and selected constituent should be reanalyzed. The acceptable ratio is:


A well mixed, measured portion of a sample is filtered through a standard glass-fiber filter and the filtrate is evaporated to dryness in a weighed dish and dried to constant weight at 180 oC. The increase in dish weight represents the total dissolved solids.


  • Evaporating dishes made porcelain,
  • platinum or high-silica glass
  • Steam bath
  • Desiccators provided with a desiccant containing a colour indicator for moisture
  • Analytical balance capable of weighing to 0.001 g
  • Filtration apparatus
  • Glass-fiber filters
  • Suction flask
  • Drying oven


A. Pre-treatment of filter and crucible

  1. Put the evaporating dishes for at least 1 hour in an oven at 180 oC. Cool and store in
    desiccators until needed. Weigh immediately before use.
  2. Prepare the glass-fiber disc by placing it, wrinkled side up, in the filtration apparatus. Apply vacuum and wash the disc with 3 successive 20-mL washings of DI water. Continue suction to remove all traces of water. Discard washings.

B. Determination

  1. Put an aliquot of sample to yield between 2.5 and 200 mg dried residue.
  2. Filter measured volume of well mixed water sample through the glass-fiber filter;
  3. Wash with 3 successive 10-mL volumes of DI water, allowing complete draining between washing.
  4. Continue suction for about 3 minutes after filtration is complete.
  5. Transfer filtrate to a weighed evaporating dish (Wtd) and evaporate to dryness on a steam bath.
  6. Dry for at least 1 hour in an oven at 180 oC, cool in desiccators, and weigh (Wtd+s).
  7. Repeat the cycle of drying, desiccating and weighing until a constant weight is obtained or until weight loss between successive weighing is less than 4 % or 0.5 mg which is less.

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