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• Building-based wastewater hydroelectric systems can offset pumping energy by 36%. • Electricity rate is the largest driver of economic value for these systems. • Annual energy generation and cost-effectiveness increase as building size increases. • These systems can act as a valuable city-scale distributed energy resource. Electricity is consumed in high-rise buildings for pumping domestic water from municipal supply lines to end users located several floors above ground level. Currently, the potential energy contained in this water is unutilized prior to being drained as wastewater to the sewer. This study assesses the potential techno-economic benefits of using a tank and turbine-generator system to recover energy from building wastewater systems. A numerical model is developed of the proposed system in the Matlab/Simscape™ environment, and simulations are conducted using measured water consumption data from a case study building located in Ottawa, Canada. An additional 2400 model scenarios are developed that correspond to buildings of varying size. Results show that the system can generate up to 1.3 megawatt hours of electricity annually; a quantity that is roughly equivalent to 36% of the building's annual domestic pumping electricity load. Additionally, the proposed system is found to be cost-effective when installed in buildings that have a minimum of 35 floors and at least 47 units per floor. However, this result is highly sensitive to the average rate of electricity charged in the building's jurisdiction. This study is novel as it is the first analysis of its kind to evaluate the techno-economic viability of building-based wastewater hydroelectric systems as a function of building size. Furthermore, the findings are important as they may be used as a tool for developers and/or policymakers for determining the viability of implementing a building-based wastewater hydroelectric system based on the building's height and unit distribution. [ABSTRACT FROM AUTHOR]