Review Reports - The Role of Water Utilities in Implementing Urban Nature-Based Solutions: An Italian Perspective

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is well written, well structured and a good topic for research, but I have the following major concerns to improve the quality:

1. The study focuses on "water utilities," but the Italian context is characterized by "multi-utilities" that often manage energy and waste alongside water. The manuscript should more explicitly define its subject. Is it strictly single-service water companies, or does it include multi-utilities where the water division is the focus? The analysis of the Urban Nature Atlas, which found involvement from "multi-utilities" but not "water utilities," suggests this distinction is critical and needs to be clarified upfront, as it may significantly impact the findings and their interpretation.
2. The sampling method for interviews is described as "snowball convenience sampling." While practical, this method can introduce selection bias, potentially over-representing certain networks or viewpoints (e.g., those already interested in NBS). The authors should acknowledge this limitation more explicitly and discuss steps taken to mitigate bias, such as seeking a diverse range of initial contacts. Furthermore, the geographic limitation to Northern and Central Italy, while noted, is a significant limitation for a study proposing a national perspective, as the South faces distinct challenges (as mentioned in 3.2.1.g). This regional bias should be emphasized in the limitations section.
3. The SWOT analysis is a useful heuristic, but its construction from qualitative interview data requires rigorous methodology to ensure reliability. The manuscript would be strengthened by a clearer description of how the themes from the inductive coding were systematically categorized into the specific Strengths, Weaknesses, Opportunities, and Threats presented in Table 1. A brief explanation of the criteria for assigning a factor as internal (S/W) vs. external (O/T) would enhance the methodological robustness.
4. Connecting Hindering Factors to Enabling Drivers: Figure 1 effectively lists hindering factors and enabling drivers, but the claim that the rows represent "the potential beneficial impacts of enabling drivers in mitigating the related hindering factors" is not visually or textually demonstrated. A more detailed discussion or a mapping table (e.g., in supplementary materials) explicitly linking specific drivers to the barriers they are designed to overcome would significantly strengthen the analytical depth and practical utility of the findings.
5. The study treats "NBS" as a monolithic category. However, the challenges, costs, and required expertise for a large-scale constructed wetland are vastly different from those for a rain garden or a green roof. The analysis would be more nuanced if it differentiated between different types of NBS (e.g., infiltration-focused vs. retention-focused, small-scale distributed vs. large-scale centralized). This could help explain why some utilities might be hesitant and provide more targeted recommendations.
6. The proposed five roles (Expert, Innovator, etc.) are a valuable contribution. However, their presentation is somewhat descriptive. The discussion would be strengthened by exploring the potential tensions or synergies between these roles. For instance, does acting as a "Funder" conflict with or complement the "Partner" role? Furthermore, the resource requirements (financial, human) for a utility to adopt these different roles are not discussed, which is crucial for practical implementation, especially for smaller operators.
7. Page 8, Line 315: "Path dependency and lack of innovation." -> This is a heading. The following paragraph repeats the sentence "Overcoming this requires a shift in skills and mindset (E20), also from municipalities, municipalities that need to think to a new concept..." -> Remove the duplicate "municipalities".
8. Page 15, Section "I": The heading is "I. Development of metrics...". For consistency with the list (a, b, c...), this should be "j.".
9. Some recent works could strengthen the literature; authors may consider the following papers.

DOI: https://doi.org/10.1016/j.ress.2025.111136

DOI: https://doi.org/10.1080/19942060.2024.2447389

Author Response

Reply to the comments by Reviewer no. 1.

We are grateful to the reviewer for their insightful feedback and constructive suggestions. We found the comments to be extremely precise and helpful, and they have significantly strengthened the manuscript. We have addressed each comment as fully as possible and revised the manuscript accordingly. Each comment is addressed in detail below

The manuscript is well written, well structured and a good topic for research, but I have the following major concerns to improve the quality:

We agree with this comment, and we have revised the manuscripts in accordance: see line 114-123 Introduction.

2. The sampling method for interviews is described as "snowball convenience sampling." While practical, this method can introduce selection bias, potentially over-representing certain networks or viewpoints (e.g., those already interested in NBS). The authors should acknowledge this limitation more explicitly and discuss steps taken to mitigate bias, such as seeking a diverse range of initial contacts. Furthermore, the geographic limitation to Northern and Central Italy, while noted, is a significant limitation for a study proposing a national perspective, as the South faces distinct challenges (as mentioned in 3.2.1.g). This regional bias should be emphasized in the limitations section.

We thank the reviewer for pointing this out. The selection of interviewees was initially based on a Report developed by REF Ricerche, as mentioned in the manuscript, for the Italian water sector, which grouped utilities according to their economic and financial performance in order to reduce potential geographical and size-related bias. This preliminary sample was then expanded through snowball sampling, allowing the inclusion of additional stakeholders identified as relevant during the interview process. In line with the suggestion, we have clarified this sampling approach in the methodology section ( line 244-252) and explicitly acknowledged its limitations in the Conclusion section (see line 1123-1127).

3. The SWOT analysis is a useful heuristic, but its construction from qualitative interview data requires rigorous methodology to ensure reliability. The manuscript would be strengthened by a clearer description of how the themes from the inductive coding were systematically categorized into the specific Strengths, Weaknesses, Opportunities, and Threats presented in Table 1. A brief explanation of the criteria for assigning a factor as internal (S/W) vs. external (O/T) would enhance the methodological robustness.

We are grateful for this valuable input. In the revised version, we have clarified that the SWOT analysis was based on a qualitative thematic synthesis of the interview data. Recurrent themes identified across participants were interpreted according to their internal or external nature (organisational vs. contextual) and positive or constraining influence on NBS implementation. These criteria guided the categorisation into Strengths, Weaknesses, Opportunities, and Threats. This specification was depicted in lines 967-981).

4. Connecting Hindering Factors to Enabling Drivers: Figure 1 effectively lists hindering factors and enabling drivers, but the claim that the rows represent "the potential beneficial impacts of enabling drivers in mitigating the related hindering factors" is not visually or textually demonstrated. A more detailed discussion or a mapping table (e.g., in supplementary materials) explicitly linking specific drivers to the barriers they are designed to overcome would significantly strengthen the analytical depth and practical utility of the findings.

Thank you for pointing this out. We accepted the comment trying to clarify better this point in lines 332-336.

5. The study treats "NBS" as a monolithic category. However, the challenges, costs, and required expertise for a large-scale constructed wetland are vastly different from those for a rain garden or a green roof. The analysis would be more nuanced if it differentiated between different types of NBS (e.g., infiltration-focused vs. retention-focused, small-scale distributed vs. large-scale centralized). This could help explain why some utilities might be hesitant and provide more targeted recommendations

We agree with this valuable observation. As this paper was conceived as an exploratory analysis, the available data did not allow for a systematic differentiation of NBS typologies. We fully acknowledge that such disaggregation—distinguishing, for instance, between small-scale green infrastructure and large-scale treatment wetlands—would yield more targeted insights and policy recommendations. However, due to the information and data available, it was not possible to properly make these distinctions in this study. This limitation, along with its relevance for future research, has now been more explicitly highlighted in the conclusion section (lines 1135–1141).

6. The proposed five roles (Expert, Innovator, etc.) are a valuable contribution. However, their presentation is somewhat descriptive. The discussion would be strengthened by exploring the potential tensions or synergies between these roles. For instance, does acting as a "Funder" conflict with or complement the "Partner" role? Furthermore, the resource requirements (financial, human) for a utility to adopt these different roles are not discussed, which is crucial for practical implementation, especially for smaller operators.

We are grateful for this valuable input. The issue of the resources required was addressed in a general way within the sections on barriers and strategies and is implicitly linked to—and influential on—the roles that utilities can effectively play. However, to address the relevant comment, this aspect, together with the mention of potential synergies and conflicts associated with these roles, was noted in lines 1037–1040. Given the exploratory nature of this study, providing further analysis here would introduce additional elements of subjectivity. Nevertheless, this interesting aspect has been highlighted among the possible avenues for future development in lines 1204–1207.

7. Page 8, Line 315: "Path dependency and lack of innovation." -> This is a heading. The following paragraph repeats the sentence "Overcoming this requires a shift in skills and mindset (E20), also from municipalities, municipalities that need to think of a new concept..." -> Remove the duplicate "municipalities".

Thank you for pointing this out. We have revised the manuscripts in accordance with deleting the redundant paragraph (see line 315).

8. Page 15, Section "I": The heading is "I. Development of metrics...". For consistency with the list (a, b, c...), this should be "j."

Thanks. Revision accepted, see line 933.

9. Some recent works could strengthen the literature; authors may consider the following papers.

DOI: https://doi.org/10.1016/j.ress.2025.111136

DOI: https://doi.org/10.1080/19942060.2024.2447389

Thank you for sharing these useful recent resources, which strengthen our literature review. We have integrated a reference to Ku Du et al. (2025) in line 54, and a reference to Danyang Di et al. (2025) in relation to NBS—as contributing to source-control measures in urban water risk mitigation—in line 57.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

General Comments

The article addresses an important and timely topic. The authors discuss challenges related to Sustainable Drainage Systems (SuDS), presenting survey results gathered from companies and experts in the field.

I would like to draw attention to the use of the term "water utilities" throughout the article. It would be more precise to use "water and wastewater utilities." In practice, there are various institutional models. In some cases, water utilities are also responsible for stormwater management, but sometimes this responsibility lies with other entities such as municipalities or dedicated wastewater or drainage authorities.

It is advisable to clarify this institutional complexity early in the article, ideally through a diagram showing:

- who is responsible for stormwater management,

- to whom the responsibility can be delegated and under what conditions (e.g. in the Italian context: public utilites, PPP, etc.),

and where ATO (Ambiti Territoriali Ottimali) and ARERA (Regulatory Authority for Energy, Networks and Environment) fit into this governance framework

Line-by-line Comments

Lines 59–60:
Please expand on the EU water policy context, specifically referencing the Water Framework Directive (WFD) and the revised Urban Wastewater Treatment Directive. Include a brief summary of the recommended measures and the environmental impact assessments related to these legislative acts.

Also, please provide more information on the methods used to promote SuDS in countries like China and Australia.

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Line 72:
Operational costs are mentioned. Please also discuss how these investments impact capital expenditures (CAPEX), and how depreciation of such infrastructure affects water tariffs.

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Line 83:
Identify the relevant institutions and agencies involved in implementing Nature-Based Solutions (NBS) in Italy. Beyond water utilities, which other actors are involved (e.g. environmental protection agencies, spatial planning bodies, etc.)?

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Line 95:
Please provide more details about the Italian water sector, particularly regarding responsibilities for rainwater management. In most EU countries, municipalities are responsible for urban water management and either delegate the task to public/private utilities or manage it through their own departments. How is this managed in Italy?

Is there any example of a private company operating stormwater infrastructure? Who finances the assets, especially regarding depreciation?

Please also describe the roles of ATO, municipalities, and ARERA, clarifying their relationships and mandates, both in general water governance and specifically in relation to rainwater. The article refers to ARERA as a regulatory authority, but it should be noted that ARERA is primarily an economic regulator. According to the OECD’s Governance of Water Regulators framework, regulation should be understood more broadly than economic regulation alone.

What other regulatory agencies are involved (e.g. sanitary inspection, environmental protection agency)? What roles do they play and what instruments do they use in the context of stormwater?

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Lines 99–101:
Please explain how water utilities can address the financing gap. Refer to Article 9 of the Water Framework Directive, which mandates cost recovery, including environmental and resource costs. Stormwater costs should be clearly allocated.

Please describe cost-recovery mechanisms used in Italy (e.g. using concept of TTT – Tariff-based, Tax-based, Transfer-based models). Are full costs for stormwater infrastructure recovered? Please include CAPEX and OPEX figures for stormwater systems in Italy if available. Can you provide an approximate amount in EUR?

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Line 161:
Could you elaborate on cases where stormwater infrastructure is financed from private funds? Are such investments made by private water and wastewater companies? If so, are these public assets? How is the return on such investments ensured when financed by private actors?

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Line 163:
Please clarify what accounts for the remaining 13% (100 - 43 - 44).

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Line 219:
Please elaborate on how the tariff-setting methodology may promote "repair and maintenance" over the implementation of NBS. Consider adding a separate section describing the Italian tariff methodology (e.g. Resolution no. 580/2019/R/IDR). Outline all tariff components and indicate which ones include NBS-related costs.Describe aby this methodology promote repair and maintanance than

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Line 222:
Regarding water tariffs in Italy: they might be lower than in some EU countries, but certainly higher than in others. Please provide average water prices in Italy and compare them with the EU average.

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Line 239:
Are there any initiatives aimed at addressing the shortage of qualified personnel? Which institutions are responsible for such efforts? Please clarify which agencies are involved in workforce development and how this is coordinated, considering that education is typically overseen by different authorities than water management.

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Line 241:
What is meant by the statement “tariff includes investment”? Does this refer to the Regulatory Asset Base (RAB) model?

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Line 315:
Municipalities are generally responsible for stormwater. Please clarify how this responsibility is handled in Italy. What methods do municipalities use to promote the adoption of NBS, and how do they participate in both investment and operational costs?

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Line 391:
Does ARERA have Key Performance Indicators (KPIs) specifically related to stormwater management? What is the role of benchmarking in ARERA's regulatory process? Does performance benchmarking influence tariff-setting?

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Line 501:
Are the listed EU funding instruments the only sources of financing for stormwater infrastructure? In many countries, structural and other eg. Structural funds play (usualy mix od UE and national) a much more significant role. Please clarify.

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Line 619:
Please suggest how ARERA could potentially incorporate sustainability obligations into its regulatory framework. In what legal act could such commitments be introduced?

While ARERA is an economic regulator, what legal mandates does it currently hold that allow it to promote sustainable practices? Who assigns ARERA its tasks (e.g. Ministry for the Environment)? What legislation defines its mission, and what current or future legal provisions could enable ARERA to take a more active role in promoting sustainable stormwater management?

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Line 802 (General Comment):
The article presents water utilities as crucial actors. However, it should be clarified that utilities often operate under mandates from municipalities and do not necessarily shape the solutions themselves. Could the article better reflect the central role of municipalities as decision-makers and initiators in this context?

Author Response

Reply to the comments by Reviewer no. 2.

We would like to thank the reviewer for the insightful feedback and useful suggestions, which have helped to strengthen this manuscript significantly. We have done our best to address each comment fully and have revised the manuscript accordingly. Each comment is addressed in detail below.

Reviewer’s comments:

We fully agree that the term “water utilities” may not accurately reflect the diversity of institutional arrangements in the water sector. We used it as abbreviation for “water and wastewater utilities” throughout the manuscript. Furthermore, we added a clarifying sentence in the introduction specifying that the term refers to entities responsible for water supply, wastewater, and—in some cases—stormwater management services. This revision ensures conceptual consistency across different governance contexts. We clarify this in line 113-121.

It is advisable to clarify this institutional complexity early in the article, ideally through a diagram showing:

- who is responsible for stormwater management,

- to whom the responsibility can be delegated and under what conditions (e.g. in the Italian context: public utilites, PPP, etc.),

and where ATO (Ambiti Territoriali Ottimali) and ARERA (Regulatory Authority for Energy, Networks and Environment) fit into this governance framework

We agree that providing a clearer explanation of governance in the Italian context is valuable. To address this point—also in response to a similar comment from Reviewer 1 and others reported below—we have added an introductory paragraph clarifying these aspects. Due to space constraints, we included a reference to a paper that illustrates this system visually. Please see the new Section 1.1 in lines 123–174.

Lines 59–60: Please expand on the EU water policy context, specifically referencing the Water Framework Directive (WFD) and the revised Urban Wastewater Treatment Directive. Include a brief summary of the recommended measures and the environmental impact assessments related to these legislative acts.

We accept this appropriate comment by adding more details on the WFD in the Introduction, line 65-76.

Also, please provide more information on the methods used to promote SuDS in countries like China and Australia.

Thank you for this suggestion. We have improved this section, but due to space constraints—also considering the addition of a substantial new paragraph—we preferred not to expand further on the international cases, and instead refer the reader to the citation provided in lines 62–66 for additional details.

Line 72: Operational costs are mentioned. Please also discuss how these investments impact capital expenditures (CAPEX), and how depreciation of such infrastructure affects water tariffs.

Thanks for this comment. We integrate further information about these aspects in the Introduction, section 1.1 in lines 123-174.

Line 83: Identify the relevant institutions and agencies involved in implementing Nature-Based Solutions (NBS) in Italy. Beyond water utilities, which other actors are involved (e.g. environmental protection agencies, spatial planning bodies, etc.)?

We appreciate this insightful comment. We develop more on actors involved in NBS development in the Introduction, section 1.1. Specifically in lines in lines 152-165.

Line 95: Please provide more details about the Italian water sector, particularly regarding responsibilities for rainwater management. In most EU countries, municipalities are responsible for urban water management and either delegate the task to public/private utilities or manage it through their own departments. How is this managed in Italy?

We accepted the comment integrating this part in the paragraph in the Introduction, section 1.1.

Is there any example of a private company operating stormwater infrastructure? Who finances the assets, especially regarding depreciation?

Thank you for pointing this out, but since the data in the ATLAS database are reported in an aggregate way it is not possible to arrive at this level of specificity.

Thanks for the comment, this is a very crucial point and we clarify the governance system under water management in Introduction, section 1.1. Lines 125-173. Also the role of ARERA as economic regulator is mentioned as a new introduction in lines 853-875.

What other regulatory agencies are involved (e.g. sanitary inspection, environmental protection agency)? What roles do they play and what instruments do they use in the context of stormwater?

Please see details on this in the new paragraph 1.1., lines 152-165

Lines 99–101: Please explain how water utilities can address the financing gap. Refer to Article 9 of the Water Framework Directive, which mandates cost recovery, including environmental and resource costs. Stormwater costs should be clearly allocated.

We are grateful for this valuable input. We have explained better the role of ARERA with particular reference to Article 9 in the Introduction, lines 176-200.

Thanks for this relevant comment. We have explained in more details the cost-recovery mechanisms in lines 176-200.

Line 161: Could you elaborate on cases where stormwater infrastructure is financed from private funds? Are such investments made by private water and wastewater companies? If so, are these public assets? How is the return on such investments ensured when financed by private actors?

Thanks for mentioning this aspect. Unfortunately, since the database used proposed only aggregated data, it is not possible to gain this level of detail.

Line 163: Please clarify what accounts for the remaining 13% (100 - 43 - 44).

We appreciate this insightful comment, and we clarified this in lines 290-294. For more details on this data, Figure S2 and S3 in Supplementary materials provide more details.

Line 219: Please elaborate on how the tariff-setting methodology may promote "repair and maintenance" over the implementation of NBS. Consider adding a separate section describing the Italian tariff methodology (e.g. Resolution no. 580/2019/R/IDR). Outline all tariff components and indicate which ones include NBS-related costs. Describe aby this methodology promote repair and maintanance than

Thanks for the suggestion. We accept this indication by adding in the Introduction the lines 176-200 explaining the function of the water tariff method.

Line 222: Regarding water tariffs in Italy: they might be lower than in some EU countries, but certainly higher than in others. Please provide average water prices in Italy and compare them with the EU average.

We are grateful for this valuable input. Please see details added on this in line 354-357 and specific note 5 in page 8, lines 359-363.

Line 239: Are there any initiatives aimed at addressing the shortage of qualified personnel? Which institutions are responsible for such efforts? Please clarify which agencies are involved in workforce development and how this is coordinated, considering that education is typically overseen by different authorities than water management.

Thanks for pointing out this relevant aspect. We integrate some initiatives related to this aspect in lines 465-471.

Line 241: What is meant by the statement “tariff includes investment”? Does this refer to the Regulatory Asset Base (RAB) model?

Yes, we have clarified this aspect and explained with more details this point in lines 176-200.

Line 315: Municipalities are generally responsible for stormwater. Please clarify how this responsibility is handled in Italy. What methods do municipalities use to promote the adoption of NBS, and how do they participate in both investment and operational costs?

Please, see new paragraph in intro about Italian context where we introduced more details on this.

Line 391: Does ARERA have Key Performance Indicators (KPIs) specifically related to stormwater management? What is the role of benchmarking in ARERA's regulatory process? Does performance benchmarking influence tariff-setting?

We are grateful for this valuable input. We introduced more details on this in lines 568-582.

Line 501: Are the listed EU funding instruments the only sources of financing for stormwater infrastructure? In many countries, structural and other eg. Structural funds play (usually mix of UE and national) a much more significant role. Please clarify.

We appreciate this insightful comment. We added details in relation to other funding sources in lines 696-711.

Line 619: Please suggest how ARERA could potentially incorporate sustainability obligations into its regulatory framework. In what legal act could such commitments be introduced? While ARERA is an economic regulator, what legal mandates does it currently hold that allow it to promote sustainable practices? Who assigns ARERA its tasks (e.g. Ministry for the Environment)? What legislation defines its mission, and what current or future legal provisions could enable ARERA to take a more active role in promoting sustainable stormwater management?

Thanks for pointing out the relevance of the role of ARERA, we added details on its role in the new paragraph on Introduction, but clarify better this specific aspect in lines 853-882

Line 802 (General Comment): The article presents water utilities as crucial actors. However, it should be clarified that utilities often operate under mandates from municipalities and do not necessarily shape the solutions themselves. Could the article better reflect the central role of municipalities as decision-makers and initiators in this context?

See the new paragraph in the Introduction that highlights this point, as well as lines 1171–1180, where we elaborate on the role of municipalities. We clarify that since utilities typically operate under municipal mandates, their capacity to implement NBS largely depends on municipal leadership, inter-institutional coordination, and the integration of NBS objectives into local planning instruments. Promoting NBS at scale therefore requires a stronger alignment between regulatory and financial incentives and the decision-making authority of municipalities.