Centralized urban water supply systems effect high social, economic, and environmental costs through large-scale treatment and distribution of potable water for all end uses. This technological regime is being challenged by climate change, population growth, and aging infrastructure. Sustainable water supply regimes which incorporate conservation, fit-for-purpose systems, and decentralized approaches can conserve freshwater resources, offset the need for new infrastructure, and reduce the energy requirements associated with treatment and pumping to meet the demands associated with increasing urbanization. There are, however, few large-scale implementations of dual systems in the U.S., and uptake of decentralized technologies in urban areas is relatively low. This is because water infrastructure, as a sociotechnical system, exists in a three-dimensional landscape of technology, society, and institutions and the transition from a centralized water management paradigm to a decentralized, fit-for-purpose regime is a major transformation which involves not only technological changes, but also changes in the momentum of behaviors, regulations, infrastructure, and symbolic meaning. The Multi-Level Perspective (MLP) is a theoretical framework which describes that transitions emerge due to interactions across three levels of society and infrastructure. At the macro-level, landscape changes in economics, cultural patterns, and policies support or inhibit transitions to new technologies. At the meso-level, regime and niche technologies interact with institutions such as communities of stakeholders, scientists, and policy makers, influencing landscape changes and supporter behavior. Finally, supporters make choices to adopt new technologies at the micro-level. The MLP can explain why innovations are adopted and can provide insight to steer sociotechnical systems toward sustainable transitions. Existing research that uses the MLP to understand water systems transitions applies qualitative case study approaches, which are limited because they cannot provide insight for new case studies to explore potential transition pathways. MATISSE is an agent-based model that was developed to represent interactions across levels of the MLP to explore potential transition pathways and was applied to simulate transition to sustainable mobility in the Netherlands. The goal of this research is to develop MATISSE for Water Supply (MATISSE-WS) by adapting the existing agent-based model to simulate the transition of a centralized water system to a dual water system that provides reclaimed water through a parallel pipe network to provide water for residential irrigation. Water reclamation represents one niche technology which challenges dominant water delivery systems. In 2001, the Town of Cary became the first water utility in North Carolina to utilize a secondary water reticulation network for providing reclaimed water to households and businesses. MATISSE-WS is applied to simulate landscape pressures in the context of water stress and public attention to simulate consumer support for reclaimed water reuse. This research validates MATISSE-WS to match data from the Town of Cary that reports new water reuse accounts from 2005 to 2015. This research demonstrates the new model, MATISSE-WS, which provides a simulation approach to understand sociotechnical transitions for water systems. MATISSE-WS can be applied to further research to explore potential transition pathways to sustainable water supply systems.
