SUMMARYEquivalent salt solution series have been previously defined as solutions with combinations of sodium absorption ratio (SAR) and electrolyte concentration (Ec) producing the same extent of clay swelling in a given soil. The present study shows that there is a high (r2>0.96) positive correlation between logEcand logSARof equivalent salt solutions series, in the equation:where a1and b1are constants for each equivalent salt solution series for a given soil.Log a1could also be represented as a linear function of b1resulting in the equation:wherea2andb2are constants for a given soil. Solving this equation using any given value ofb1yields the combinations ofSARandEcwhich make up each equivalent salt solution series for a given soil. The relationship between log a1andb2for three soils from western United States, namely Waukena, Pachappa and Grangeville, was similar, with their combined data having ar2value of 0.96. This indicated that a single set of equivalent salt solution series values could be used for these three soils which have different clay contents and clay mineralogy.Prediction of hydraulic conductivity decreases withEcreduction at given values ofSARin red‐brown and alluvial soils from southern Tasmania, using the equivalent salt solution series values for Waukena soil, showed similar patterns to measured values and also to those predicted using the equivalent salt solution values applicable to the respective Tasmanian soils.Thus, available data indicate that the same set of equivalent salt series could be applied to the five soils studied. If further testing shows that a single set of equivalent salt solutions values could be applied to all or large groups of soils, this would facilitate the application of the equivalent salt solution concept to predict salt solution flow in the fiel