Determination of Total Dissolved Solids (TDS) in water and wastewater

This procedure covers the determination of total dissolved solids (TDS) in wastewater prior to treatment and disposal to marine outfall (inlet and outlet effluents of ETP) and applicable at the laboratory.


  • Collect 1 litre of sample to a clean polythene carboy, label the container and deliver it to the lab. Shake the contents of the container thoroughly before drawing the sample for testing.
  • Draw a measured volume of sample quickly from the container.
  • Transfer the sample to a clean and pre-weighted evaporating dish and evaporate to dryness in an oven at 180oC
  • Cool the dish in a desiccator to an ambient temperature and re-weight it
  • Calculate the TDS in mg/lit, using formula.

Total dissolved solids/TDS (mg/lit) =

(Final weight of dish – the Initial weight of dish) ×10^6/Sample volume (ml)

  • Record the measurements and the results.