This study presents a decision support tool that evaluates the environmental efficiency of reusing treated wastewater for agricultural irrigation, among other options. The developed tool is published as open source at https://doi.org/10.18167/DVN1/YLP1BA. The objective of this decision support tool is to facilitate the interpretation of the Life Cycle Assessment (LCA) results by progressively reducing the non-discriminatory impacts to solve the difficulty of making a decision with a large number of criteria. This framework was applied to a representative case of reuse of reclaimed water for vine irrigation at the Murviel-Les-Montpellier experimental site (Hérault, France). It was then generalized through modeling assumptions to consider different reuse scenarios. To highlight situations in which the supply of recycled water for irrigation may or may not provide significant environmental benefits, four main parameters were varied: (i) tertiary treatment technologies, (ii) availability of conventional water sources, (iii) energy mix composition. The results show that the environmental impact of treated wastewater reuse depends directly on the type of tertiary treatment technology and the location of the treatment plant in relation to the field and other water sources. The decision support tool has identified where wastewater reuse is clearly an environmentally beneficial source of irrigation among surface and groundwater sources (e.g., WWTP closer to field than river, groundwater too deep, tertiary treatment environmentally beneficial). However, there are many situations where the decision support process cannot distinguish between reuse of treated wastewater for agricultural irrigation and conventional water sources, especially when the nutrient content of treated municipal wastewater is insufficient to offset the negative effects of high energy requirements and chemicals of tertiary treatment.