An empirical method of determination of the activity coefficients and activities was applied to the binary H2O-H2SO4 system. This component-based treatment was shown to give thermodynamically consistent definitions and satisfy the Gibbs-Duhem equation under the entire concentration range, unlike most molality-based and ionic interaction models. The selection of the reference state is important, and any derivations from the experimental data must follow thermodynamic rules. The empirical functions are extendable to the whole concentration range, including areas where water is not a solvent.