WaCSim: A water and cyber co-simulation framework for enhancing cyber security in smart water systems

Smart Water Distribution Systems (WDSs) are physical water networks whose pumps, valves, and tanks are operated through a digital layer of sensors, Programmable Logic Controllers (PLCs), and Supervisory Control and Data Acquisition (SCADA) systems. This connectivity improves operational efficiency but also exposes critical water infrastructure to cyber-attacks. Studying how to operate such systems resiliently requires simulators that reproduce both the hydraulic process and the control network. Existing cyber-physical testbeds, however, are largely passive: they model a single control architecture and record how an attack manifests, without letting an operator's defense logic act while the attack unfolds. We introduce WaCSim (Water and Cyber Simulation), an open-source cyber-physical co-simulation framework that addresses this gap. WaCSim couples the EPANET hydraulic engine with an emulated industrial control network (Mininet and MiniCPS), introducing two critical capabilities. First, it supports decentralized (PLC-to-PLC), centralized (SCADA), and hybrid control within a single framework. In hybrid mode, a PLC receives the same physical measurement via two independent paths, enabling attackers to target them differentially and exposing semantic conflicts that single-architecture tools cannot represent. Second, it establishes the defender as an active, in-loop actor, allowing researchers to embed custom control, detection, and conflict-resolution algorithms directly into the simulation loop to actively alter the hydraulic trajectory as an attack progresses. Through case studies, we demonstrate how WaCSim models cyber-attacks, evaluates defense mechanisms, and supports the development of intelligent control systems. These examples illustrate WaCSim's utility as a research and development platform for advancing the robustness, security, and operational intelligence of smart water networks.