BOMI Air Handling, Water Treatment & Plumbing Systems Practice Test

Conductivity measures how well water conducts electricity, which rises with the concentration of dissolved ions. TDS is the total amount of dissolved solids, most of which become ions in solution. Because the amount of dissolved ions drives conductivity, you can estimate TDS from conductivity values rather than measuring solids directly. In practice, a conversion factor is applied: TDS (mg/L) ≈ conductivity (µS/cm) × factor, with the factor depending on the water’s ion composition (commonly around 0.5 to 0.7 for many freshwater samples). This is an approximation, since some nonionic substances don’t affect conductivity much and highly saline waters may require a different factor. pH, on the other hand, reflects acidity/alkalinity and does not indicate how much dissolved solid is present, which is why TDS is estimated from conductivity rather than measured by pH.