Potash mining is one of the most significant industries in Canada and an important part of Saskatchewan’s economy, as potash is a leading commodity by the value of production. During the last decade, there has been an increased number of new potash mine developments and expansion projects within the province. A new solution mine started its operation in May 2017 and five more mines are either under construction, or will be by 2020. All mines but one will utilize a solution technique for ore extraction, and solution potash mining is heavily reliant upon water availability. Currently there is a sufficient amount of fresh water available within Saskatchewan for potash production, however this could change as a result of climate change and variability. In the last 50 years, since potash mining was introduced to Saskatchewan, there has not been a drought longer than one or two years, but the paleohydrology from tree-rings reveals that droughts within the region can last for a decade or longer. This research was conducted to examine how climate change could affect the water supply of solution potash mining in southern Saskatchewan. The South Saskatchewan River Basin (SSRB) and the Qu’Appelle River Basin (QRB) runoff was projected using output from a large ensemble of regional climate models (RCMs) from the NARCCAP and CORDEX scientific programs. The observed runoff and its annual cycle over 1971-2000 was simulated using seven different runoff estimation methods, total runoff (mrro), surface runoff (mrros), four aridity indices (Budyko, Ol’dekop, Schreiber and Turc) and statistical downscaling, in order to identify the best two estimators of observed runoff. Based on the quantile indicators of goodness of fit, total runoff (mrro) and the statistical downscaling based on the standardized precipitation evapotranspiration index (SPEI) are the best estimation techniques for the SSRB, and were used to project the 21st century runoff within the basin. None of the estimation methods could simulate the runoff of the QRB, which is a highly managed waterway. Based on mrro projections, the water supplies in southern Saskatchewan would remain relatively constant with possible dramatic changes in the seasonal distribution of flow. SPEI projected severe drying, but the methodology might require further improvement. Such severe drying could lead to water conflicts, and should be considered during development of expansion projects and new potash mines. Keywords: aridity index, climate change, CORDEX RCMs, NARCCAP RCMs, potash, projected changes, runoff, solution potash mining, South Saskatchewan River Basin, standardized precipitation evapotranspiration index (SPEI), Qu’Appelle River Basin