The Turc-Mezentsev water balance formula is a simple and efficient mathematical formulation relating long-term average streamflow to long-term average precipitation and potential evaporation. Usually, it is applied in its original form, i.e., without parameterization. This paper aims to assess the possibilities of regionalizing this formula for improved efficiency on ungaged catchments. Four regionalization options are compared based on: (i) the relative error, (ii) the arithmetic difference, (iii) the correcting factor of the aridity index, and (iv) the shape factor. The four alternatives are assessed in terms of efficiency and robustness on a large set of 609 French catchments. We show that introducing a correcting factor of the aridity index provides the best regionalization solution.