Introduction

Urban water systems are among the most sensitive elements of critical infrastructure because disruption to their operation can immediately affect public health, social stability, and the continuity of essential services. Drinking water treatment plants are particularly important, as they depend on continuous operation, complex treatment processes, chemical handling, electromechanical equipment, and monitoring and control systems. These features expose them not only to natural hazards but also to deliberate human-made threats such as sabotage, cyber intrusion, intentional contamination, disruption of energy supply, and interference with treatment processes. Such events may reduce water quality, interrupt production, create public health emergencies, and weaken public confidence in urban services.

Conventional protection measures mainly emphasize physical security and emergency response. Although necessary, these measures do not fully show whether a facility can absorb disruption, recover its functions, and learn from the event. Resilience offers a broader framework by considering resistance, recovery, and adaptation together. However, much of the available literature on water resilience focuses on natural hazards or distribution networks, while quantitative assessments of treatment plants under deliberate threat scenarios remain limited. This study therefore evaluates the resilience of an urban drinking water treatment plant against human-made threats using the Critical Infrastructure Elements Resilience Assessment method (CIERA). It also identifies the main technical and organizational weaknesses requiring improvement.



Methodology

The research was applied in purpose and descriptive–analytical in design. A quantitative, indicator-based approach was used to assess the current condition of the selected treatment plant. For security reasons, the name and detailed characteristics of the facility are not reported. The study followed the three main phases of the CIERA method: preparation, assessment, and analysis and improvement.

During the preparation phase, the facility was described in structural and functional terms, and relevant threats were identified through technical documents, operational reports, safety instructions, literature review, and expert consultation. Based on expert agreement, deliberate biological or chemical contamination caused by sabotage in treatment or transfer processes was selected as the main scenario. Possible pathways included unauthorized manipulation of treatment units, intrusion into control and monitoring systems, intentional injection of contaminants, and interference with chemical dosing.

Data were collected through document review, semi-structured interviews, and specialized CIERA questionnaires. Five experts participated, representing urban water systems, operation and maintenance, critical-infrastructure risk and safety, crisis management and security, and passive defence. Items were scored independently on a five-point Likert scale and then normalized, weighted, and aggregated using the CIERA equations.

Three resilience components were assessed. Robustness covered crisis preparedness, redundancy, detection capability, operational response, and physical resistance. Recoverability included material, financial, and human resources, together with recovery processes. Adaptability examined risk management, innovation, and staff education and development. Component scores were expressed as percentages, and overall resilience was calculated as the mean of the three components. Under the CIERA classification, 85–100% indicates high resilience, 69–84% acceptable resilience, 53–68% low resilience, 37–52% undesirable resilience, and 36% or less a critical condition.



Results and discussion

The treatment plant received a robustness score of 73.02%, placing this component in the acceptable range. Physical resistance and operational response were among the stronger areas, indicating that the plant has a reasonable capacity to withstand the initial effects of a deliberate disruption and maintain essential functions. However, threat detection and crisis preparedness received lower evaluations. These weaknesses are important in a contamination scenario, where delayed identification may allow the incident to spread before corrective action begins. Improved real-time monitoring, access control, anomaly detection, and threat-specific exercises would strengthen the plant’s early response.

Recoverability was scored at 71.25%, also within the acceptable range. Human and financial resources were evaluated relatively positively, suggesting that personnel and funding could be mobilized after an incident. In contrast, formal recovery procedures and integrated planning were less developed. Available resources cannot ensure rapid restoration unless roles, priorities, communication channels, and operational sequences are defined in advance. Recovery plans should therefore be documented, tested, and coordinated with technical teams, security units, public-health authorities, and urban crisis managers.

Adaptability received the lowest score, at 63.08%, and fell within the low category. Staff education and development showed a comparatively better condition, but risk management and organizational innovation remained weak. The plant therefore appears better prepared to resist and recover from a known event than to learn from experience and adjust to emerging threats. Limited institutional learning may allow weaknesses identified during exercises or incidents to persist. Insufficient investment in technological and managerial innovation may also reduce preparedness for new cyber-physical or combined threats.

The overall resilience score was 69.12%, placing the facility at the lower boundary of the acceptable category. This result should not be interpreted as full security. It indicates that existing technical and recovery capacities provide a useful foundation, while long-term adaptation remains the main constraint. Since the three components are interconnected, improving adaptability may also enhance future robustness and recoverability. Lessons learned from exercises can strengthen detection and response procedures, while systematic risk assessment can guide investment in monitoring, redundancy, and emergency resources.



Conclusion

The CIERA method provided a structured way to assess both technical and organizational resilience under a deliberate contamination scenario. The plant showed acceptable robustness and recoverability, whereas adaptability remained below the acceptable threshold. Priority actions include institutionalizing risk management, improving detection and crisis preparedness, documenting and testing recovery plans, and strengthening organizational learning and innovation. These actions should form part of a continuous resilience cycle rather than isolated corrective measures. The findings can assist water-utility managers, urban planners, security authorities, and passive-defence organizations in prioritizing interventions and allocating resources. Although the study concerns one facility and one principal scenario, the approach can be adapted to similar treatment plants if local operating conditions, threat profiles, and organizational capacities are considered.