What method can be used to measure total dissolved solids (TDS) in water?

• A. TDS is measured by tasting the water for saltiness.
• B. TDS is determined by measuring dissolved oxygen levels.
• C. TDS is measured using a refractometer to assess total dissolved solids.
• D. TDS can be measured by conductivity to estimate ion concentration or direct gravimetric analysis after filtration.

Answer: (D)

Total dissolved solids are the mix of dissolved ions and other substances in water. Because many of these substances are charged particles, they conduct electricity. A conductivity meter uses this principle to give a fast, practical estimate of how many solids are dissolved, which researchers convert into a TDS value. For a direct measurement, you can filter the water and weigh the solid residue after drying it—this gravimetric method gives the actual mass of dissolved solids present.

Tasting the water isn’t reliable or safe, and dissolved oxygen levels tell you about gas content, not solids. A refractometer measures how light bends to estimate concentration for specific substances like sugars or seawater salinity, but it doesn’t reliably quantify the diverse mix of dissolved solids in general water samples. That’s why using conductivity (or gravimetric analysis after filtration) is the appropriate approach for measuring TDS.