Smart cities are envisioned to efficiently use two most critical resources: water and energy. Advanced techniques are being developed to conserve water and to minimize the use of conventional energy. The integration of battery energy storage (BES) technology and renewable energy (RE) sources in the system is very much required to enable the efficient coupling and modularization of electricity and water infrastructure. This chapter presents a conceptual framework to demonstrate an Internet of Things (IoT)-based intelligent hardware-software platform to efficiently manage the most critical infrastructure in sustainable smart cities: water and energy technologies. The integrated framework focuses on the challenges of water-energy nexus. It includes advanced technologies for metering and communication, and computational intelligence using machine learning techniques in purview of the infrastructural constraints for optimal integration of BES and RE source. Towards developing the conceptual framework, the systematic approach of developing an intelligent hardware-software platform is presented in this chapter. The proposed framework will be deployed in the smart city test bed at Gujarat International Finance Tec-City (GIFT), India. Test bed for water-energy nexus includes water treatment plant (WTP), sewage treatment plant (STP), and street lightings connected with BES and solar photovoltaic (PV) generation. We also discuss the use cases towards water-energy nexus that will be implemented in this framework. The intellectual merit of the framework is the development of hardware-software technology platform—comprising a set of common knowledge, theoretical approaches, mathematical models, optimization, and analytical tools—that will contribute in making possible the promising environmentally sustainable smart city.