The present study, as the first study of this type in Iran, was carried out with the aim of modeling Water–Energy‐Environment nexus of Jajrood River in northern Iran. The water evaluation and planning and long‐range energy alternative planning software were used as practical tools for water and energy modeling. To this end, after collecting the required input data on water and power supply and demand in Jajrood Basin, with regard to the population increase rate, three scenarios were simulated. By linking the data of the two software, the overlap between supply and demand in the nexus between water and energy, and greenhouse gas emissions were compared. According to the results, “reducing water consumption” (first scenario) and “rising water prices” (second scenario) were the best scenarios for policy‐making in the fields of water, energy, and environmental conservation in the next 20 years. These two scenarios will have four benefits of reducing water consumption (32.9 and 16.52%, respectively, under the first and second scenarios), reducing energy consumption (32 and 14.4%, respectively, under the first and second scenarios), reducing power generation (1.87 and 81.8%, respectively, under the first and second scenarios), and reducing greenhouse gas emissions (25 and 11%, respectively, under the first and second scenarios).