A novel methodology to develop EU water reuse risk management plan in agricultural water distribution networks and crop irrigation systems

A novel methodology to develop EU water reuse risk management plan in agricultural water distribution networks and crop irrigation systems Pietro Drei a,* , Giuseppe Mancuso a , Stevo Lavrni´ c a , Roberta Maffettone b , Massimo Spizzirri c , Luisa Merluzzi c , Alessandra Mastrantonio c , Paolo Burla d , Attilio Toscano a a Alma Mater Studiorum - University of Bologna, Department of Agricultural and Food Sciences, viale Giuseppe Fanin 50, Bologna 40127, Italy b Joint Research Centre, European Commission, via Fermi 2749, Ispra I-21027, Italy c Acea Ato 2 S.p.A., Piazzale Ostiense 2, Rome 00154, Italy d Consorzio di Bonifica Litorale Nord, Via del Fosso di Dragoncello, 172, Casalpalocco, Rome 00124, Italy ARTICLE INFO Key words: Water reuse Wastewater Risk assessment Reclaimed water Agriculture irrigation ABSTRACT Treated wastewater (TWW) can be used as an additional water resource to overcome global water scarcity. In response, the EU introduced Regulation 2020/741, which establishes minimum requirements for using TWW in agriculture. In addition, the regulation requires the formulation of a risk management plan for every TWW reuse case and for the entire reuse system. While assessments and management before the outlet of the reclamation facility are well-established, there is limited experience developed for the part of the system beyond the outlet of the reclamation facility. To perform this assessment, new stakeholders (e.g. water distribution managers, storage operators, farmers), previously often overlooked, need to be involved. This study introduces an innovative methodological framework for developing and implementing a risk management plan beyond the outlet of the reclamation facility, focusing mainly on the irrigation distribution network that delivers TWW to its final use in crop irrigation. The approach includes a strategic appraisal using a qualitative method to characterize risks and ensure safe and sustainable water reuse. It also identifies critical nodes within the reuse system, addressing both Human Health Risk Assessment and Environmental Risk Assessment. This methodology was applied on a comprehensive case study in central Italy, where the potential reuse of TWW was assessed for agricultural irrigation in a real 26,000-hectare district. The study represents one of the largest and most complex potential scenarios faced by irrigation managers and operators in Italy. The findings from the risk assessment suggest that the application of tailored, site-specific preventive measures can substantially mitigate associated risks. Glossary Environmental Risk Assessment (ERA) – Evaluation of potential impacts from chemical and physical contaminants on environmental compartments (soil, groundwater, surface water) associated with the use of treated wastewater for irrigation. Environmental Sensitivity (ES) – Indicator of the vulnerability of environmental receptors, based on site-specific characteristics (e. g., hydrogeology). Hazardous event – An operational or environmental incident (e.g., treatment failure, pipe break) that may introduce a hazard into the reuse system. Human Health Risk Assessment (HHRA) – Assessment of microbiological risks to human health associated with the use of treated wastewater for irrigation. Key Risk Management Elements (KRMs) – Core components outlined in Regulation (EU) 2020/741 to structure water reuse risk assessments and management plans. Likelihood of occurrence (LO) – Estimated probability that a hazardous event will occur in the system. Probability of exposure (PE) – Likelihood that a receptor (environmental compartments) will come into contact with a given hazard. Reclamation facility – Treatment unit that improves TWW up to the quality required for irrigation reuse. * Corresponding author. E-mail address: [email protected] (P. Drei). Contents lists available at ScienceDirect Water Research X journal homepage: www.sciencedirect.com/journal/water-research-x https://doi.org/10.1016/j.wroa.2025.100395 Received 24 June 2025; Received in revised form 31 July 2025; Accepted 3 August 2025 Water Research X 28 (2025) 100395 Available online 5 August 2025 2589-9147/© 2025 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/bync-nd/4.0/ ). Risk Management Plan (RMP) – Site-specific plan required by Regulation (EU) 2020/741 to identify, assess, and manage risks throughout the water reuse chain. Severity of hazard (S) – Estimate of the potential impact of a hazard, depending on its nature and the sensitivity of the exposed receptor. Wastewater Treatment Plant (WWTP) – Facility that treats wastewater and may include reclamation steps for reuse. 1. Introduction As global water scarcity continues to escalate, it is projected that by 2050, 40 % of the world’s population will be living in regions experiencing severe water shortages (García-Valverde et al., 2023; UN-Water, 23 2020). This challenge will impact particularly water-scarce areas, such as arid and semi-arid regions (Mancuso et al., 2023; Ofori et al., 2021). Additionally, water pollution exacerbates the crisis, further limiting available freshwater resources (Nan et al., 2023). In fact, nearly 70 % of global water consumption is directed toward agricultural crop irrigation in dry and semi-dry regions worldwide (Ofori et al., 2021; Ventura et al., 2019). The reuse of TWW for agricultural purposes is gaining global traction as a sustainable solution (Mancuso et al., 2024; Singh, 2021). However, despite its potential, only about 20 % of the TWW generated worldwide is currently reused, while the remaining part is released into the environment (Christou et al., 2024). Improper TWW management poses risks due to residual contaminants, potentially impacting persons, the environment, and entering the food chain (Yalin et al., 2023). The consequences of exposure can vary widely, from immediate concerns for workers and nearby populations to more gradual environmental degradation affecting soil and water resources quality. Furthermore, contaminants can potentially enter the food chain through irrigation, leading to foodborne illnesses or long-term health effects (Singh, 2021). To mitigate these risks, the European Union introduced the Regulation (EU) 2020/741, which sets minimum water quality requirements for the reuse of TWW in agricultural irrigation (Berti Suman et al., 2023; Regulation (EU) 2020/741, 2020). Regulation 2020/741 requires the development of a comprehensive risk management plan to protect human and animal health and the environment. This plan must cover the entire water reuse system, from the inflow of wastewater to the treatment plant to its application in agricultural irrigation (Regulation EU 2020/741, 2020). Recently, technical guidance on developing a risk management plan has been published (Maffettone and Gawlik, 2022). Risk assessment is a central component of these management plans. Three risk assessment approaches can be used: quantitative, semiquantitative, and qualitative. Quantitative risk assessments are applied when precise numerical data on hazards, exposure pathways, and potential impacts are available (Cantoni et al., 2021) for example in wastewater treatment plants (WWTPs) and reclamation facilities (Roeger and Tavares, 2018). This method allows for a detailed probabilistic analysis, providing a numerical estimation of the likelihood and severity of adverse effects. On the other hand, semi-quantitative and qualitative risk assessments integrate qualitative insights with limited quantitative data to characterize and prioritize risks, and specific methodological frameworks have recently been developed for water reuse applications (Carnesi et al., 2025; Rebelo et al., 2022; Vidotti et al., 2024). They can be utilized when a quantitative approach is not feasible due to limited data availability, such as in distribution networks, storage systems, and on-field irrigation. In certain parts of the water reuse system (e.g. irrigation channels, pipelines), quantitative approaches may be challenging due to the lack of data and the variability of environmental and agricultural conditions across these vast areas. These components of water reuse systems are managed by different stakeholders such as irrigation district managers, distributors, storage operators, and farmers. Many of these stakeholders may be unfamiliar with the risk management provisions introduced by the Regulation 2020/741 and they typically lack experience in quantitative risk analysis, which consistently complicates data collection efforts. For distributors and storage operators, the primary objective is to ensure a consistent supply of irrigation water across extensive areas and they tend to focus mostly on addressing drought conditions (Ricart et al., 2024). Consequently, their emphasis lies more on monitoring volumetric data than water quality, especially given the current absence of regulatory standards for irrigation water quality (Yalin et al., 2023). The absence of water quality data in these parts of the systems together with limited involvement of these stakeholders in risk management plans, constitutes a significant challenge. This is particularly relevant when alternative water sources such as TWW are used for irrigation. In this case, water quality of reclaimed water needs to be clearly communicated for the awareness and knowledge necessary for the risk assessment phase. Furthermore, in the absence of comprehensive monitoring data, qualitative methodologies such as semi-structured interviews and complementary questionnaires can be utilised for data collection. These methods are more appropriate for the involvement of stakeholders, as the collection of information is based on their experiential insights and on-site observations of typical behaviours. This approach helps identify attitudes and actions on practises of crop irrigation necessary for the development of risk management plan in water reuse systems (Ronco et al., 2017). Given that the Regulation 2020/741 mandates the development of a risk management plan across the entire water reuse system, this study presents a novel and adaptable risk management methodology applicable to the components downstream of the reclamation facility (e.g., distribution network, storage system, on-farm irrigation). This methodology aims to evaluate the potential risks of TWW reuse even to extensive distribution network, from the outlet of the reclamation facility to final use in field irrigation. The proposed methodology is developed based on input from key stakeholders, integrating new actors across the water reuse system and employing semi-structured interviews to extract critical information and insights from their expertise. It is tailored to any site-specific conditions and relies on primary data that are typically available, providing a robust and adaptable tool that can be applied in different areas, even when the data availability is scarce. The overall methodology is briefly outlined in Materials and Methods (Section 2.2), fully detailed in the Results (Section 3.2), and its application to a real full-scale case study is presented in Section 3.2. 2. Materials and methods 2.1. Overall risk management framework The proposed risk management methodology aims to enhance and broaden the risk analysis conducted within WWTPs and the reclamation facility. It focuses on the distribution and irrigation components of the water reuse system downstream from the reclamation facility (i.e., distribution network, storage system, on-farm irrigation) but does not include post-harvest activities or consumer exposure. While the JRC technical report (Maffettone and Gawlik, 2022) outlines the Key Elements of Risk Management (KRMs), it does not provide a defined methodology but rather general recommendations particularly lacking in guidance on Environmental Risk Assessment (ERA), particularly in complex systems. In developing the methodology, we integrated complementary elements from the sanitation safety planning (WHO, 2022), the Australia Guidelines for Water Recycling (2006), ISO 20426 (2018), and the JRC technical report (Maffettone and Gawlik, 2022), which collectively provided operational structures, regulatory context, and technical criteria to support both the health and environmental dimensions of risk assessment. The present methodology builds upon P. Drei et al. Water Research X 28 (2025) 100395 2 these suggestions, specifically aiming to address the existing gaps (e.g. lack of practical guidance for assessing environmental risks and assigning qualitative values to risk parameters in complex irrigation systems). It proposes a comprehensive method to evaluate the potential health and environmental risks that integrate data analysis and interviews, starting from the description of the water reuse system (Phase 1), identification of hazardous events, exposed groups and exposure pathways (Phase 2), risk assessment (Phase 3) until the identification of preventive measures (Phase 4) (Fig. 1). Each step of the methodology is described and systematically detailed in the Results section (Section 3.2). The risk analysis was conducted using a qualitative approach, employing two distinct assessment models to evaluate human health and environmental risks in alignment with the KRMs framework (Maffettone and Gawlik, 2022): 1. Human Health Risk Assessment (HHRA) addresses all hazardous events that carry microbiological risks for people involved. 2. Environmental Risk Assessment (ERA), assessing risks to surface water, groundwater, and soil due to chemical-physical contaminations within the study area. In this study, the HHRA focuses on microbiological hazards, particularly for irrigators and farmers exposed to TWW in open distribution networks, considering the system boundaries, monitored contaminants in TWW, and acute effects of pathogens on human health. Meanwhile, the ERA evaluates chemical and physical contaminants in TWW. By addressing chemical contaminants for environmental risks, the ERA concurrently protects human health by mitigating potential indirect exposure pathways in an integrated approach (Maffettone and Gawlik, 2022; Pensierini et al., 2024; Rebelo et al., 2022). To align the assessment with site-specific characteristics, a new variable Environmental Sensitivity (ES) was introduced (Section 3.1.3), enabling a more accurate evaluation of environmental hazards and supporting integrated human health protection. To manage risks effectively, a two-tiered risk assessment approach, as outlined in the Australia Guidelines for Water Recycling (2006) was Fig. 1. Risk management framework, four phases. P. Drei et al. Water Research X 28 (2025) 100395 3 employed. The first step is to establish the maximum risk, which is the level of risk without preventive measures. Residual risk, which is the remaining risk after applying existing preventive measures, provides insight into the scheme’s safety and sustainability, indicating whether further measures are needed. Based on the results of the residual risk, the second step foresees the development of preventive measures to minimize the risk to an acceptable level, as per the requirements of Regulation EU 2020/741. Even though this research shows the methodology application on a specific study area, it was primarily designed to be applicable to different types, sizes and complexities of water reuse systems. Its modular structure, high flexibility and reliance on limited primary data make it suitable for adaptation to diverse operational contexts, even in data-scarce conditions, enabling targeted risk analysis focused on the most critical components according to site-specific conditions. 2.2. Study area The Fregene WWTP, managed by ACEA ATO 2 and located in the Lazio region (Italy) (Fig. 2), has a capacity of 76.000 PE and includes tertiary treatment technologies (e.g., sand filtration, UV disinfection) for the enhancement of influent quality. During the monitoring period (from 2020 to 2024), an average daily discharge volume of the Fregene WWTP was 10,54 m 3 . In the study area, the irrigation network managed by the Irrigation Consortium “Consorzio della Bonifica Litorale Nord” (CBLN), includes 69 irrigation districts, which are primarily supplied by the Tevere river, and, to a lesser extent, by the smaller Arrone river. About 16,70 ×10 6 m 3 of freshwater (99.5 % and 0.5 % from Tevere and Arrone rivers, respectively) is withdrawn annually. Water withdrawals occur from March to November and are used for crop irrigation, with the highest water demand during the summer season. Currently, freshwater is withdrawn and first conveyed to the irrigation channels (total length of 24.4 km), before being collected in a water reservoir (total capacity of 180,000 m 3 ). A piping system (total extension of 114.4 km), either before or after the storage, is used for further water distribution for irrigation (Fig. 2). Irrigation can occur at any stage within the distribution network using irrigation channels or pressurized piping systems. The pressurized piping system operates on demand during the irrigation season, allowing farmers to irrigate according to their individual schedules and crop needs. The primary agricultural production is oriented toward herbaceous, horticultural, and forage crops, which collectively represent 97.7 % of the total cultivated area (data from the CBLN database covering the 2020–2022 period). 2.3. Data collection The TWW quality data were collected and analyzed in collaboration with the responsible party for the Fregene WWTP. Additionally, volumetric data on irrigation water withdrawn and distributed, infrastructural details of all the components within the distribution systems, and geo-spatial data on the irrigation district, including crop types and irrigation methods, were gathered in collaboration with the CBLN. For the environmental characterization (e.g. groundwater level, soil type), data utilized were obtained from open-source datasets, specifically the Geoportal of the Lazio region (https://geoportale.regione. lazio.it/), the ARSIAL portal (https://www.arsial.it/) and the ARPA Lazio portal (https://www.arpalazio.it/). In the absence of comprehensive monitoring data, qualitative methods such as semi-structured interviews are effective for engaging stakeholders, as they draw on experiential knowledge and direct observation of routine practices (Ronco et al., 2017). This approach is widely accepted to integrate insufficient data, and it was recommended by Australia Guidelines for Water Recycling (2006) and later adopted by Lane et al. (2022), Ronco et al. (2017), and Vinti et al. (2023). Stakeholder interviews play a central role in collecting accurate and context-specific information for the risk assessment. In the current study, the technical director and operators from the Fig. 2. Location of the Fregene WWTP and Distribution and Irrigation district. P. Drei et al. Water Research X 28 (2025) 100395 4 company responsible for irrigation water distribution participated in the risk assessment through a series of semi-structured interviews. This company also represents the farmers who receive the irrigation water and therefore can convey their experiences. Additionally, the technical director, operators, and laboratory manager from the company overseeing the Fregene WWTP served as advisors in the risk assessment process. The information provided was reviewed carefully and, where possible, supported by technical documentation (e.g., number of system failures detected by remote monitoring systems) and validated through targeted field visits. These inspections, conducted together with system operators, focused on elements such as the irrigation method used (e.g., sprinkler or drip), the distance between agricultural fields and residential areas, and the presence of physical protection measures (e.g., fences or warning signs). This integrated approach allows for a comprehensive and site-specific understanding of the system’s critical nodes. 3. Results and discussion 3.1. Development of risk management methodology 3.1.1. Water reuse system description The description of the water reuse system (Phase 1) (Fig. 2) should cover each component of the system beyond the outlet of the reclamation facility, including the TWW storage and distribution, as well as the irrigation methods and the crop type. Key nodes include pumping stations, control structures, and essential components of the distribution system. The aim of the water reuse system description is to define these key nodes based on infrastructural, volumetric, and geo-spatial data collected. 3.1.2. Identification of hazardous events, exposed groups and exposure pathways Identifying hazardous events is a crucial step in risk evaluation (Phase 2) (Fig. 2). A hazardous event is an incident or situation that can lead to the presence of a hazard (Australia Guidelines for Water Recycling, 2006). Hazardous events can vary in nature, ranging from single processes to a series of linked events, and may occur both during regular system operation, as well as due to system failure or accident, or as a result of weather conditions. For HHRA, all hazardous events that can cause contact between TWW and the human population in the area were identified for each node of the reuse system. HHRA identifies specific exposed groups (e.g. distribution system workers, agricultural workers, local community) that may come in contact with TWW through inhalation of aerosols, ingestion of contaminated materials, or dermal contact. Similarly, for ERA all hazardous events are identified for each node where TWW could inadvertently come into contact with an environmental compartment (i.e. surface water, groundwater, soil) through different pathways, such as surface runoff or infiltration. In each identified key node of the water reuse system, a list of preliminary hazardous events was developed, based on infrastructural details, geo-spatial data of the irrigation district and literature findings (Australia Guidelines for Water Recycling, 2006; Maffettone and Gawlik, 2022). The preliminary hazardous events served as input for semi-structured interviews with the technical director and operators from the company responsible for irrigation resource distribution. During these interviews, the preliminary hazardous events were validated for each key node, and, if necessary, additional hazardous events were identified and added. The finalized list was then shared with the technical staff of the company overseeing the Fregene WWTP for further discussion and validation. 3.1.3. Risk assessment The risk assessment (Phase 3) (Fig. 2) of the methodology adopts two distinct approaches: one for the HHRA and another for the ERA. 3.1.3.1. Human health risk assessment (HHRA). The HHRA was conducted by calculating the microbial risk level as defined in Eq. (1). Each hazardous event was assessed by assigning a score to the Likelihood of Occurrence (LO), representing the probability of the event occurring, and to the Severity of Hazard (S), indicating the potential adverse health effects resulting from exposure. Risk(R) = Likelihood of Occurrence(LO)x Severity of Hazard(S)(Eq. 1) LO and S were assigned based on the JRC guidelines and the criteria are given in Table S1 and Table S2 of the supplementary materials (Maffettone and Gawlik, 2022; ISO 20426, 2018). LO for each hazardous event was evaluated and given a value from 1 to 5, based on whether the event was deemed "very unlikely", "unlikely", "possible", "probable" or "very probable". Similarly, each event was rated for S, with values from 1 to 5 depending on whether the hazard was considered "insignificant", "minor", "moderate", "major" or "catastrophic". A second round of semi-structured interviews was conducted with the technical director and operators from the CBLN. Starting from the predefined list of hazardous events, LO and S of each event were assessed with experts who were asked to justify their choices. The interview outputs were critically evaluated by integrating field observations and relevant scientific literature, after which they were also discussed with the technical staff of the Fregene WWTP. Once the values for the LO and S were determined, Eq. (1) was applied to calculate the risk, ranging from 1 (minimum) to 25 (maximum), and categorized as "low", "medium", "high" or "very high" (Table S3 of the supplementary materials). This initial risk assessment was conducted under a maximum risk scenario, assuming no preventive or mitigation measures are in place. 3.1.3.2. Environmental risk assessment (ERA). The ERA was performed by determining the risk level through a combined assessment of the Probability of Exposure (PE) and the Severity of Hazard (S), as defined in Eq. (2). In the ERA, each hazardous event was connected to an impact on various environmental compartments (surface water, groundwater, soil) depending on the exposure pathway. Due to the extreme heterogeneity of these elements, they were evaluated separately, and different risk assessments were associated with each identified hazardous event based on the environmental exposure group concerned. Moreover, it was also essential to account for the intrinsic characteristics of the environmental system; therefore, ERA was modified by introducing an additional variable, the Probability of Exposure (PE), which reflects the likelihood of pollutants present in the TWW reaching environmental compartments. This likelihood was based on the probability of occurrence of a hazardous event with potentially harmful effects and the site-specific characteristics of the assessed exposure groups. Risk(R) = Probability of Exposure(PE)x Severity of Hazard(S)(Eq. 2) The risk analysis matrix (Table S3, of the supplementary materials), developed from the sanitation safety plan matrix (WHO, 2022) and consistent with HHRA, was used for this purpose. The R level, with a maximum value of 25, can then be classified as "low", "medium", "high" or "very high". The S of a hazardous event was assessed qualitatively based on factors including the size and nature of the exposed population, exposure route, amount, and duration (Australia Guidelines for Water Recycling, 2006). For each event values ranging from 1 to 5 were assigned to the factor S (Table S4 in the Supplementary materials), based on whether the hazard was considered "insignificant", "minor", "moderate", "major" or "catastrophic" (Table S4 of the supplementary materials). Moreover, the LO for each hazardous event was evaluated (Maffettone and Gawlik, 2022; ISO 20426, 2018) and assigned a value from 1 to 5, based on whether the event was deemed "very unlikely", "unlikely", "possible", "probable", or "very probable"(Table S1 of the P. Drei et al. Water Research X 28 (2025) 100395 5 supplementary materials). The PE, was calculated as reported in Eq. (3): Following the same approach used in the HHRA, in the second round of semi-structured interviews with field engineers, operators, agronomists, and the technical director from CBLN, LO and S, for each hazardous event identified were assessed. The interview outputs were also discussed with the technical staff of the Fregene WWTP and critically reviewed based onthe field observations and relevant scientific literature. The Environmental Sensitivity (ES) represents a site-specific evaluation of the environmental conditions surrounding the water reuse system, taking into account the key characteristics of the environmental compartment that influence its susceptibility to pollution. While the physicochemical properties of contaminants (e.g., pKa, hydrophobicity, molecular structure) are also important determinants of environmental fate, these data are often not available and considering them would limit the practical applicability of the methodology in data-limited contexts. To each of the three identified environmental compartments (i.e. surface water, groundwater, soil), an ES class from 1 to 4: "low", "medium", "high", and "very high" (Table 1) was assigned, based on environmental data analysis using QGIS and field observations. For surface water, the ES value depended on the likelihood of contaminants present in TWW to reach a surface water body, considering the irrigation method and the characteristics of the agricultural drainage system (ISO 20426, 2018; Maffettone and Gawlik, 2022). For groundwater, the ES value depended on the site’s hydrogeological conditions (e.g., the presence of an aquifer), the likelihood of contaminants moving to the unsaturated zone through infiltration, and the irrigation conditions. Soil was also considered in groundwater sensitivity assessments based on its clay content (ISO 20426, 2018; Maffettone and Gawlik, 2022). As for soil, classification was performed by considering soil texture and organic matter content, following methodologies reported in the literature (Aydi et al., 2016; Francaviglia et al., 2017). This choice was made since soil texture significantly impacts its permeability, influencing the way that pollution seeps through it. Sandy and sandy loam soils with high permeability are unsuitable for waste disposal, whereas sandy clay and clay loam soils with lower permeability levels are more appropriate(Aydi et al., 2016). Additionally, soil organic matter (SOM) is a crucial indicator for determining soil quality, providing valuable insights into its overall health and fertility (Francaviglia et al., 2017). On the other hand, crop type is not included in this assessment due to a large spatial and temporal variations of the agricultural practices. When water reuse network serves multiple fields with different crops, that also change yearly due to crop rotation, it is extremely impractical to integrate crop-specific effects at the system scale. Table 1 includes sensitivity classifications for surface water and groundwater derived from ISO standards (ISO 16075–1, 2020), with the addition of soil sensitivity to the assessment. As a result, a matrix (Table S5 of supplementary materials) was then developed to divide the results into five categories of PE, with a maximum value of 20 and classified from 1 to 5, depending on whether the identified event and the environmental compartment were considered "very unlikely", "unlikely", "possible", "probable" or "very probable". 3.1.4. Development of preventive measures The risk assessment framework adopts a two-tiered approach to guide the development of preventive measures (Phase 4) (Fig. 1). The first tier identifies the maximum risk by pinpointing the most hazardous event at each key node, crucial for initial system screening and prioritization. Stakeholders managing components beyond the discharge point(e.g. irrigation water managers, farmers), often lack experience in risk management but may already employ infrastructure, maintenance protocols, or irrigation practices. These, even though they may have been designed for other purpose, can also function as preventive measures in water reuse systems and can reduce the likelihood of hazardous events (LO). The list of key nodes and standard preventive measures (Maffettone and Gawlik, 2022) informed a third round of semi-structured interviews with the technical staff of the company responsible for irrigation resource distribution. Experts described existing measures at each node, which were then independently assessed, including their effectiveness based on relevant literature. Each hazardous event was evaluated to determine whether existing measures could reduce its LO, and residual risk was then calculated. Based on this assessment, all events with medium, high or very high residual risk were selected, and site-specific preventive measures were developed. These tailored actions, grounded in the standard measures list, enable risk reduction to acceptable levels across the critical nodes identified. Table 1 Assignment of the environmental sensitivity (ES) (partly based on ISO (ISO 16075‑1, 2020)). Sensitivity group (ES) Surface water Groundwater Soil 1 Low Presence of a deep drainage system (at >80 cm) There is no aquifer under the irrigated area and there is no hydrogeological continuity that could allow water passage to a nearby aquifer. Texture: clay and clay loam soil Soil organic matter (SOM) (%): >2,0 2 Medium The design and operation of the irrigation system prevent surface runoff. Presence of an aquifer at a depth of >5 m with a clay content of >40 % in the last 2 m of soil. Texture: clay loam, loam and clay sandy loam, loam Soil organic matter (SOM) ( %): >1,5 3 High The design and operation of the irrigation system prevent surface runoff. Presence of a shallow underground drainage system (at a depth of 80 cm or less). Presence of an aquifer at >5 m depth from the surface, with a clay content of between 15 and 40 % in the first 2 m of soil. Texture: limosum soil, limosum loam Soil organic matter (SOM) ( %): >1,0 4 Very high Presence of surface runoff during irrigation or surface accumulations that can wash during rainy events. Presence of a notconfined aquifer under the irrigated area with clay content (2) <5 % in the last 2 m of soil; Presence of an aquifer at a depth of <5 m. Texture: sandy, sandy loam and sandy loam Soil organic matter (SOM) ( %): <=1,0 Probability of Exposure(PE) = Likelihood of Occurrence (LO)x Environmental Sensitivity(ES)(Eq. 3) P. Drei et al. Water Research X 28 (2025) 100395 6 3.2. Application of the risk management methodology 3.2.1. Water reuse system description The water reuse system, still in the planning stage, will involve conveying the TWW produced at the Fregene WWTP into an irrigation channel located upstream of the CBLN irrigation network. For this purpose, a 3.5 km pipeline has been designed but not yet implemented, to connect the outlet of the reclamation facility to the irrigation channel, with a maximum flow rate of 250 L s -1 . Although the mean contribution of TWW to the total water withdrawal during the irrigation season is approximately 17 %, a detailed monthly analysis reveals that in early and late irrigation periods, specifically in March and November, TWW volumes can fully replace freshwater withdrawals, with TWW/V ratios of 106 % and 177 %, respectively. The use of TWW offers strategic and economic advantages, as it allows the water reuse system to sustain irrigation when surface water availability is lowest, reducing pressure on conventional sources and enhancing the overall resilience of the irrigation network. Moreover, both ACEA ATO 2 and CBLN preferred to perform the risk assessment for the whole system before starting with a large-scale water reuse system. The water reuse system was divided into two sub-systems for risk management purposes. The first include wastewater collection and treatment up to the outlet of the reclamation facility. The second covered the water reuse system, from the WWTP outlet through the pipeline and irrigation distribution network to the agricultural fields. System boundaries were defined accordingly: HHRA applies to the entire system due to potential human exposure throughout, while the ERA focuses only on the second sub-system. Although a comprehensive risk management plan was developed for both sub-systems, this study concentrated on the water reuse system from the point where TWW exits the WWTP to its irrigational use. Fig. 3 presents the system boundaries and all the key nodes identified from the water reuse system description. Node P1 represents the actual point where WWTP discharges TWW into surface water (Arrone river), and node P2 marks the point of compliance for the water reuse system before TWW enters the distribution network. Although this is often not the case, in this particular system, these two points do not coincide since they are separated by a short water channel. Regarding TWW quality, the Fregene WWTP currently meets the standards for surface water discharge under Italian Legislative Decree No 152/2006. The current risk assessment is conducted in compliance with Regulation (EU) 2020/741. Although not yet fully optimized for reuse, 81 % of 196 samples (2020–2022) showed Escherichia coli concentrations <100 CFU/100 mL, compliant with Class B under Regulation EU 2020/741. The WWTP is planned to be upgraded with additional disinfection technology and, once it is operational, the effluent is expected to meet Class A standards (10 CFU/100 mL). Monitoring of 60 contaminants of emerging concern revealed only five (e.g., PFBA, estrone, carbamazepine) at concentrations well below environmental thresholds, confirming good effluent quality for safe agricultural reuse. Considering the potential of TWW to increase irrigation water resources, two scenarios for further evaluation were identified. The first scenario, based on the current operational status of the WWTP which is currently producing Class B quality TWW in accordance with Regulation EU 2020/741, focuses on the identification and mitigation of risks through the implementation of appropriate preventive measures. The second scenario projects a future state in which the WWTP achieves the more stringent Class A quality standards in accordance with Regulation EU 2020/741. In both scenarios, the TWW from the Fregene WWTP is intended to be combined with conventional irrigation water, thereby serving as a supplementary irrigation resource. 3.2.2. Identification of hazardous events, exposed groups and exposure pathways The hazardous events were divided in two categories: 1) actual events linked to risks inherent in the existing infrastructure or system characteristics and 2) potential events pertaining to risks that may arise from the planning and subsequent operationalization of new infrastructure. Fig. 4 shows the populations exposed to potential risks at each node of the water reuse system. Moreover, it specifies the environmental compartments at risk and delineates the pathways of contamination, as they are pertinent to the ERA. The Table 2 and Table 3 list the main hazardous event for each key node and the complete list is included in the risk matrix (see supplementary materials). Fig. 3. System boundaries in the water reuse system scheme. P. Drei et al. Water Research X 28 (2025) 100395 7 3.2.3. Risk assessment 3.2.3.1. Human health risk assessment results. The outcomes of the risk analysis have classified the 21 identified hazardous events according to their level of risk for the human health. The first risk assessment resulted in the maximum risk (Table 2), and it does not take into account already applied preventive measures. The analysis revealed that one event is associated with a very high risk (i.e. the access to the main surface irrigation channel by the local community and passersby and accidental or deliberate contact with the TWW), seven hazardous events with a high risk, two events with a medium risk, and eleven are associated with a low risk (Table 2). 3.2.3.2. Environmental risk assessment. The assignment of Environmental Sensitivity (ES) classes is a prerequisite for evaluating environmental risk levels. This section characterizes the key site-specific features required for risk assessment of surface water, groundwater, and soil. In this case, the primary limitation was the non-uniform spatial distribution of environmental monitoring data, which was addressed by processing existing datasets in a GIS environment and applying spatial interpolation to unmonitored areas. Despite the approximations involved, the resulting outputs were essential for ES attribution. For improved resolution, expanding the monitoring network within the reuse area is recommended. Surface water sensitivity was assessed based on interviews with technicians from the CBLN and a field visit that revealed that drainage systems in the study area are predominantly superficial or shallow. Accordingly, an ES class of 3 was assigned, reflecting potential connectivity between surface runoff and local water bodies. The reuse system spans five distinct hydrogeological complexes. Fig. 5 presents interpolated data from groundwater monitoring points, indicating that approximately 80 % of locations showed no detectable water table. However, equipotential line analysis (Fig. 5B) identified a continuous aquifer in the coastal zone at depths of 5–20 m. Given this depth and the presence of a 15–40 % clay layer in the upper 2 m of soil, the aquifer was assigned an ES rating of 3. This finding contrasts with initial assumptions of minimal aquifer presence, suggesting a potentially vulnerable zone within the reuse system. The lithological context was found to be heterogeneous, dominated by gravel-sand-clay formations. Soil texture information, shown in Figure 5(C), was interpolated from available data and categorized into ES classes: 1 (clay, clay loam), 2 (loam-silty clay, loam-sandy clay), 3 (silty, silty loam, loam), and 4 (sandy, sandy loam). A central zone near the Fregene WWTP falls under ES class 4. Regarding soil organic matter (SOM), Figure 5(D) indicates that values are predominantly ≤1 % across the irrigation districts. Based on the combined low SOM and highpermeability texture, the overall ES classification for the area was conservatively set to class 4, indicating high susceptibility to contaminant transport. For each hazardous event, depending on the environmental compartment at risk, an LO, ES, and S were assigned (for the complete matrix, see supplementary materials). The introduction of ES enabled assigning a risk score to each hazardous event for every affected environmental compartment. The risk analysis have classified the 16 hazardous events in total, and their maximum risk was calculated (Table 3). Considering these evaluations, none of the hazardous events were categorized as very high risk. Four events fell into the high-risk category, 20 were deemed medium risk, and 24 were considered low risk. The events that attained a high-risk level include unintentional losses from the farm distribution network’s pressure pipeline and accidental leakages due to bank or bottom breaches in the surface channels of the secondary distribution network (Table 3). Development of Preventive Measures Fig. 4. Vulnerable populations, environmental compartments, and exposure pathways in the water reuse system. P. Drei et al. Water Research X 28 (2025) 100395 8 In agricultural irrigation, environmental risks are mainly related to chemical and physical factors, which are largely managed at the reclamation facility’s outlet by monitoring specific parameter concentrations. However, human health risks are primarily associated with pathogens and can be mitigated throughout the TWW system, from the reclamation facility’s outlet to its final use in field irrigation. Preventive measures are guided by internationally recognized technical guidelines that evaluate pathogen risk reduction through treatment and nontreatment barriers, promoting a multi-barrier approach to meet health-based performance targets (ISO 16075‑1:2020; WHO, 2006). 3.2.3.3. Existing preventive measures. Once the first risk evaluation was obtained, information on existing preventive measures aimed at reducing the LO of the considered event was integrated, and information from the system analysis and expert interviews with Irrigation Consortium experts was also considered. For HHRA, existing control measures primarily consist of a remote monitoring and warning system that detects failures in the pressurized network. However, privately managed irrigation network lacks any such controls, representing a critical weakness. Although public access to the main surface irrigation channel is officially prohibited, the absence of physical barriers or warning signs means that potential exposure remains unchanged, leaving initial risk scores unaffected. In the subsystem of surface distribution channels, the managing private company has recently begun constructing a pressurized pipeline network to replace open channels. While promising, this infrastructure is not yet operational and does not currently reduce risk. Moreover, sprinkler irrigation is the dominant method in the reuse area. Compared to drip systems, sprinklers increase the likelihood of accidental exposure to TWW for both workers and nearby communities, limiting opportunities to lower risk thresholds. After integrating system observations and existing controls into the risk assessment of 21 human health-related hazardous events, residual risk levels were recalculated. The outcome showed one event at very high risk, six at high risk, two at medium risk, and twelve at low risk (Table 2), indicating a moderate risk reduction compared to the initial assessment. Further details are available in the supplementary materials. As for ERA, the risk of 16 initially identified hazardous environmental events was reassessed following the evaluation of existing preventive measures and supporting observations. Out of 48 original risks, after the reassessment, no event is associated with a very high risk. 2 events fell into the high-risk category, 20 were deemed medium risk, and 26 were considered low risk (Table 3). 3.2.3.4. Tailored preventive measures. For HHRA two TWW reuse scenarios were examined for revaluating risks for human health and establishing additional preventive measures. The first scenario, called "Risk Integration with Preventive Measures", acknowledges the current status of the Fregene WWTP, which continues to produce water of Class B quality, according to EU 2020/741. Within this framework, for each hazardous event associated with a very high, high, or medium level of risk, a set of preventive measures was recommended to mitigate these risks. The preventive measures developed are closely linked to the critical nodes of the water reuse system identified through the risk Table 2 Human health risk assessment results, ranged from 1 (minimum) to 25 (maximum). Sub-system Node Hazardous event Consequences Maximum Risk Residual Risk Connecting pipeline Connecting pipeline Unintentional water loss Spillage of TWW, exposure to pathogens 4 4 Distribution network Surface channels Surface channels - Primary distribution channel Unintended or deliberate channel entry Direct exposure to TWW 10 10 Entry into channel area 16 16 Sediment Accumulation Channel obstruction, increased flood potential 3 2 Unauthorized Discharges Degradation of TWW quality, exposure to pathogens 5 5 Surface channels - Secondary distribution channels Unintended or deliberate channel entry Direct exposure to TWW 10 10 Entry into channel area 12 8 Sediment Accumulation Channel obstruction, increased flood potential 3 2 Unauthorized Discharges Degradation of TWW quality, exposure to pathogens 5 5 Distribution network Pressure pipeline Primary distribution network Unintentional Loss Spillage of TWW, exposure to pathogens 4 4 Secondary distribution network 6 4 Farm distribution network 10 10 Storage systems Storage systems Unintended or deliberate entry into water Direct exposure to TWW 5 5 Unauthorized activity near the storage 4 4 Unauthorized Discharges Degradation of TWW quality, exposure to pathogens 5 5 Sediment Accumulation Storage obstruction, increased flood potential 3 2 Formation of biofilm Degradation of TWW quality, exposure to pathogens 9 9 Unintentional Loss Spillage of TWW, exposure to pathogens 4 4 Distribution facility Distribution facility System Failure Spillage of TWW, exposure to pathogens 4 4 Irrigation system Irrigation system Direct Access to the irrigated area Direct exposure to TWW 12 12 System Failure Spillage of TWW, exposure to pathogens 15 15 Maximum Risk: the level of risk in the absence of any preventive measures; Residual Risk: the level of risk remaining after the application of existing preventive measures. Existing preventive measures (e.g., maintenance, remote control system, and drainage system). P. Drei et al. Water Research X 28 (2025) 100395 9