The WSP model (Water Safety Plan)

The WSP model pursues a risk assessment and management approach based on integrated control measures extended throughout the entire drinking water supply chain, aimed at protecting source water resources and controlling the system and processes to ensure, over time, the absence of potential physical, biological, and chemical hazards in water intended for human consumption.

The proposed approach, which modifies and evolves the criteria for controlling water intended for human consumption, became mandatory in Italy in 2017 with the issuance of Ministerial Decree (DM) June 14, 2017, transposing Directive (EU) 2015/1787. In 2020, the new Directive (EU) 2020/2184 on the quality of drinking water established the obligation for all European Union (EU) Member States to implement a preventive risk assessment and management system, which was transposed into Italian law by Legislative Decree (DL.vo) 18/2023.

According to the provisions of the new decree, Regions, Autonomous Provinces, and drinking water operators, each within their respective competencies, must ensure that the supply, treatment, and distribution of water intended for human consumption follow a holistic risk-based safety approach. This approach is described in Article 7 of the new Directive and consists of three elements:

• The risk assessment and management of the water withdrawal areas for the water intended for human consumption must be carried out for the first time by July 12, 2027, and reviewed at periodic intervals not exceeding six years (Article 7 of the decree);

• la valutazione e gestione del rischio delle aree di alimentazione dei punti di prelievo di acque destinate al consumo umano deve essere effettuata per la prima volta entro il 12 luglio 2027 e riesaminata a intervalli periodici non superiori a sei anni (art. 7 del decreto);

• The risk assessment and management of the drinking water supply system must be carried out for the first time by January 12, 2029, and reviewed at periodic intervals not exceeding six years (Article 8 of the decree);
• The first risk assessment of the internal water distribution systems within the building must be carried out by January 12, 2029, and reviewed every six years (Article 9 of the decree).

In this context, the Italian National Institute of Health (ISS) and the Ministry of Health, in collaboration with the World Health Organization (WHO), have brought about a significant evolution in the criteria and methodologies for implementing Water Safety Plans (WSPs). This evolution aims to enhance the effectiveness and efficiency of risk-based approaches in water systems.

This advancement is outlined in the national guidelines for WSP implementation (ISTISAN 22/33), which represent a revision of the guidelines originally published in 2014.

To develop a Water Safety Plan, it is necessary to:

• Divide the water supply system into sections (storage, well, treatment, etc.)
• Classify the hazardous events that may occur
• Define the intrinsic risks of the system (i.e., assess the severity of potential hazardous events) based on the hazard category (chemical contamination, microbiological contamination, etc.) and the type of section (storage, well, etc.)
• Evaluate the likelihood of each hazardous event occurring in each section
• Determine the risk matrix by calculating the risk index (likelihood of occurrence multiplied by the severity of the event) for each hazardous event in each section of the system

Based on the risk matrix (classifying risk indices into categories: low from 0 to 5, medium from 6 to 9, etc.), it is possible to identify which mitigation actions should be implemented and in what order of priority. These actions aim to reduce the probability of specific hazardous events occurring in particular sections, thereby lowering the risk index and achieving a downgrade of the associated risk level.