Spatial variation in willingness-to-pay for wastewater system modifications: The Mille-Îles River as a case study

Pressures on water resources are intensifying worldwide, particularly in urban areas where urbanization and climate change are reducing the efficiency of water management systems. In Quebec, outdated systems exacerbate these issues, leading to wastewater discharges during extreme weather events. Modernizing these systems is essential to prevent resource degradation and promote environmental, economic, and health benefits. Hybrid water management systems, which combine centralized and decentralized approaches, are a promising solution. However, challenges such as social acceptability and significant investment requirements limit the modernization of these systems. This study assesses residents' preferences for wastewater system modifications and their willingness to pay, focusing on spatial differences along the river. Using a Discrete Choice Experiment conducted via LimeSurvey, we analyzed preferences across 25 watershed cities and Laval, located on the opposite bank of the Mille-Îles River. Attributes include reduced river restrictions, system coverage, infrastructure impact and associated costs. We developed a Mixed Logit model to assess respondents' willingness to pay for hybrid management systems, while accounting for preference heterogeneity and analyzing spatial differences. Our main findings suggest that upstream respondents are more willing to pay for treatment plant modifications that better preserve river water quality than downstream respondents.