Four empirical equations describing the temperature dependence of electrical conductance of aqueous solutions are compared for the case of single electrolytes. The best method uses a modified Walden product where the log of the ratio between the conductances at two temperatures is assumed to be proportional to the log of the corresponding ratio of viscosities, that is, log (X(sub t sub 1)/X(sub t sub 2)) = K log (eta (sub t sub 2)/eta (sub t sub 1)). A basis for predicting the constant of proportionality for mixed systems given the ion concentrations is proposed and the dependence of ionic strength effects and ion association is discussed. The value of K may also be estimated from the hydrogen ion concentration (in micromoles per liter) where K = 0.941 - 0.00639(H(1+)) as found by regression of data for 692 lakes. A case study of time trend data for lakes is presented. (Copyright (c) 1987 by the American Chemical Society.)