Nexushaus is a new residential housing prototype that is responsive to the challenges of the energy-water “nexus” in the context of growth in the United States from Texas all the way west to California. Nexushaus offers residents the following features: A modular design system that can change as residents’ needs change over time, smaller, well designed interior spaces combined with generous outdoor living spaces, a photovoltaic array designed for maximum efficiency and flexibility, a hydronic air conditioning and heating system, a potable rainwater collection system with integrated thermal storage and a greywater garden irrigation system.