Conductivity is a measurement of the ability of water to transmit electricity due to the presence of dissolved ions. Absolute pure water with no ions will not conduct an electrical current. Conductivity is measured by a conductivity meter and is reported as micromhos/cm or microSiemens/cm. Conductivity is a convenient method of determining the level of ions in a water but is non-specific in what the ions are. The electrical conductance of ions will vary by ion and will decrease as the concentration of ions increase. TDS (Total Dissolved Salts) meters utilize conductivity measurements with a conversion factor applied. Conductivity can also be estimated using individual conversion factors from the reported ion concentrations of a water analysis or by using a single conversion factor based on the sum of the ions (TDS).

         Carbon dioxide conductivity can be estimated by taking the square root of the ppm concentration and then multiplying by 0.6. The silica ion does not contribute to conductivity. The most accurate conductivity readings for high quality RO permeate are obtained on-site since carbon dioxide levels, being a gas, can vary when exposed to the atmosphere.