Abstract – This report considers several theoretical aspects and practical applications of specific conductance to the study of natural waters.

A review of accepted measurements of conductivity of secondary standard 0.01 N KCl solution suggests that a widely used algorithm for predicting the temperature variation in conductivity is in error. A new algorithm is derived and compared with accepted measurements. Instrumental temperature compensation circuits based on 0.01 N KCl or NaCl are likely to give erroneous results in unusual or special water, such as seawater, acid mine waters, and acid rain.

An approach for predicting the specific conductance of a water sample from the analytically determined major ion composition is described and critically evaluated. The model predicts the specific conductance to within +/- 8 percent (one standard deviation) in waters with specific conductances of 0 to 800 S/cm. Application of this approach to analytical quality control is discussed.

Comments – Ronald L. Miller has significantly revised the original algorithm in the original 1988 report described here so that he can now link specific conductance and concentrations of major ions in natural waters from about 30 to 54,000 S/cm with good accuracy. This allows quality assurance (QA) checks between cation sum, anion sum, field specific conductance, and laboratory specific conductance for a wide range of natural waters including seawater. This is offered as part of an expert system that gives brief English-language QA information in an Excel spreadsheet for reviewing major-ion data, specific conductance data, and dissolved solids data. It is available on a CD from Chem-Hydro Science and Consumer Products, LLC, in Tampa, Florida.