Threat Assessment of Intentional Contamination of Water Resources and Passive‐Defense Strategies for Protecting Urban Water‐Supply Systems

The protection of urban water‐supply systems against deliberate harm sits at the intersection of two policy debates: how states designate, finance, and protect critical infrastructure, and how the cybersecurity agenda should extend to the operational technology running everyday public services. Water policy nonetheless still regulates utilities through instruments written for accidental failure rather than adaptive adversaries, and this study addresses that mismatch. Focusing on urban water‐supply systems in Iran, it identifies, assesses, and prioritizes the intentional threats against them, emphasizing intentional contamination of water resources, and proposes passive‐defense mitigation. The research is applied and descriptive–analytical. Data were collected through a structured literature review and a single‐round expert‐panel survey of 12 Iranian specialists in water engineering, water hygiene, crisis management, and infrastructure security. Threats were scored on a Risk Assessment Matrix (RAM) using probability, consequence severity, and difficulty of detection and control (Cronbach's α = 0.87; ICC = 0.81; Fleiss' κ = 0.74). Biological and chemical contamination, cyber‐attacks, informational–psychological threats, and hybrid threats emerged as the most important hazards, and surface sources, intakes, reservoirs, treatment plants, and control systems as the most vulnerable components. For Iran, the study recommends a mandatory minimum passive‐defense baseline—online quality monitoring, enforced access control, SCADA segmentation and audit, and a preauthorized crisis‐communication protocol with a named custodian—because these address the four highest‐scoring threats within existing budgets and mandates. More broadly, an informational–psychological threat can rank alongside chemical contamination, implying that communication capacity should be financed and audited as security infrastructure.