Awareness of the importance of policy regarding the equitable distribution of global water resources is increasing. The purpose of this research study was to investigate the effects of allocation rules and drought conditions on allocation decisions through a decision experiment based on an idealized river basin that simulated conditions in the Saskatchewan River Basin. Participants took on the roles of water managers responsible for allocating water resources to four competing sectors in Alberta, Saskatchewan, and Manitoba. Three variations of allocation rules were tested: (a) status-quo allocation rules mimicking the current governance structure involving prearranged allocation rules across regions, (b) no predetermined rules, and (c) no predetermined rules but communication among participants. Each allocation rule was tested under two potential water levels: (a) drier-than-average conditions today reflecting 81% of historical flows, and (b) severe drought conditions with a 45% reduction from today’s flows. Results showed that policy had a significant effect on how participants allocated water resources, indicating that the absence of defined minimal flow rules and the lack of communication among riparian users resulted in less equitable distribution of water, with negative ramifications for downstream users. Additionally, results showed that drought-induced water scarcity significantly affected allocation patterns, with participants choosing to protect municipal water use at the expense of industry and agriculture in the face of water shortage conditions. For decision makers and water stakeholders in the Saskatchewan River Basin, these findings provide insight into the effectiveness of the 1969 Master Agreement on Apportionment to ensure the equitable distribution of water through defined minimum flows and the problem of fragmented governance, which prevents effective communication between upstream and downstream users. The findings also highlighted the importance of having a formal rule structure to oversee allocations or ongoing communication processes to facilitate problem solving in preparation for drought conditions.