Optimization of the Water–Energy–Carbon Nexus in the Residential Water Uses of Shanghai, China

Round 1

Reviewer 1 Report

The Authors explore the topic of water-energy nexus with specific reference to residential water consumption. The manuscript is clear and well written, and the topic of this work fully fits the themes and the scopes of the MDPI Sustainability journal. I congratulate the Authors for this interesting work, the quality of which  is almost eligible for publication. I have only some minor suggestions to further enhance the quality and the fluency of this manuscript. Please find my comments below:

• The “Introduction” section is very well written (indeed, one of the best I have read on this topic). My only suggestion is to enhance the literature review on residential water consumption with specific reference to the issue of water conservation. Indeed, some recent works have extensively reviewed the past studies focusing on water conservation with specific reference to the residential sector and at the level of individual end uses of water. The authors can refer, by way of example, to the study by Mazzoni et al. (2023) attached below (in which a specific section is devoted to those studies focusing on water conservation and efficiency) but also to the references of the above study.

• In the “Materials and Methods” section, I did not find consistency between the phases of the study shown in Figure 1 and those described in the text. I suggest the authors to rethink Figure 1 by enhancing the correspondence with method phases, while disregarding all the details which are not essential at the very beginning of the section, when describing the general method layout.

• Lines 146-157. I suggest the Authors to provide more details about the “questionnaire survey”. A discussion of the main characteristics and layout of the developed water-use survey will help Readers who are potentially interested in applying a similar strategy to investigate residential uses of water.

• Table 1. I believe that the table would benefit from a note about the meaning of the word “upgrade” when applied to conservation behaviours. Do “showerhead upgrade” and “faucet upgrade”  mean tap replacement with a more efficient one (e.g. with a lower flow rate)? Similarly, does “toilet upgrade” means the replacement of toilet tank with a cistern with limited capacity or a dual-flush system? The same note should be provided for the energy and the water-and-energy conservation strategies.

• Table 2 (and hereinafter in the text). Please refer to water-use “duration” instead of “length”.

• Table 3 and Figure 2. Would it be possible to add information about monthly water consumption (cubic meters/household/month or liters/household/month) in addition to the monthly water fee? This would make this case study of great interest for researchers and practitioners interested in investigating the characteristics of water consumption in different contexts worldwide.

• Figure 3. These results are in line with those reported by most studies on residential end uses of water shown in the review by Mazzoni et al. (2023) and the related references. I believe that results similarity should be acknowledged by the Author, in order to further demonstrate the robustness of the results achieved through the questionnaire.

• Figure 4b. This figure is very informative, and it really represents one of the key-findings of this study. I appreciate the way in which results are shown (and the same applies to Figure 8b). However, the development of the acronyms in the legend could help the Reader in better interpreting the results achieved without the need to shift to Table 1. Lastly, I could not find any mention to the acronym SHU appearing in the figure – is it the same as SU?

• Lines 356-361. Again, I suggest including the acronyms adopted in Figure 6 also in this part of text in order to help the Reader better understand the results.

• I appreciate the “Potential improvements in future research” section (in which the main study limitations are drawn) and the brief summary of study findings available in the “Conclusions” section. However, I believe that this latter section would benefit from a brief, conclusive discussion on the implications that this research and the related results may have for water-energy-gas utilities, practitioners, and all the other subjects involved in the field of water-energy resources management. Are there any practical short- and long-term applications of these findings? How can these findings support water-gas-energy utilities in a better resource management, along with citizens in resource conservation?

Suggested References

Mazzoni, F., Alvisi, S., Blokker, E. J. M., Buchberger, S. G., Castelletti, A. F., Cominola, A., Gross, M. P., Jacobs, H. E., Mayer, P. W., Steffelbauer, R. A., Stillwell, A. S., Tzatchkov, V., Yamanaka, V. H., and Franchini, M. 2023. “Investigating the characteristics of residential end uses of water: a worldwide review.” Water Research, 230(Feb), 119500. https://doi.org/10.1016/j.watres.2022.119500

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The work is submitted as a research paper. It presents a study which analyses the structure of households water consumption through a comprehensive survey and proposes a season-based water-energy-carbon nexus model coupled with Monte Carlo simulation aimed at the minimization of cost associated with water and energy usage while minimizing carbon emission.

The article is coherent with the subject coverage of the journal and the topic is interesting. English language is fine and only a slight revision is required. The structure works well.

I have not major comments and only some suggestion are provided in the following.

- A space is almost always missing before citations in the text. Please, fix this throughout the manuscript.

- Page 3, line 99: the expression "commences" is not suitable and should be replaced with an alternative expression (for example, "is based on").

- Page 3, line 106: "an" should be replaced with "a".

- Page 4, line 140: please, introduce the acronym GDP.

- Page 5, line 205: the term "greater" seems to be inappropriate, p-value should be lower than 0.05 to consider the test. Please, clarify this aspect.

- Page 7, line 258: "surpass" can be replaced with "overcome". 

Minor editing of English language required. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript presents a comprehensive study on optimizing the water-energy-carbon nexus in residential water uses in Shanghai, China. This research is of significant relevance given the pressing global challenges of water scarcity, energy consumption, and carbon emissions. The authors' efforts to construct a season-based optimization model coupled with Monte Carlo simulation are commendable, as they provide a robust framework for assessing potential savings in water and energy consumption and associated carbon emission reductions.

The study addresses an essential and timely topic by exploring the interconnectedness of water, energy, and carbon emissions at the urban household level in Shanghai, a representative of modernized large cities in China. The methodological framework, integrating questionnaire surveys with an optimization model and Monte Carlo simulations, is well-conceived and executed, providing valuable insights into household water and energy consumption patterns and potential for carbon emission reduction. The findings offer actionable insights for policymakers and urban planners regarding the promotion of water-saving appliances and the adoption of energy-efficient behaviors among residents, which are critical for achieving sustainability goals.

Areas for Improvement:

Clarification of Abbreviations: It is noted in the manuscript annotations that certain abbreviations (mentioned in section 2 and Table 1) were unclear to the readers. A straightforward list of abbreviations or a glossary section at the beginning or end of the manuscript could greatly enhance readability and understanding.

Survey Details: The manuscript annotates a question regarding the specifics of the questionnaire survey (e.g., number of questionnaires, company involved). It would be beneficial to provide a more detailed description of the survey design, distribution, and response rate to strengthen the validity of the survey results.

Economic Feasibility of Recommendations: The manuscript suggests potential annual savings per household but also highlights an annotation questioning the sufficiency of these savings. It would be advantageous to explore and discuss the economic feasibility and scalability of the recommended conservation actions further. Investigating larger-scale implications and cost-benefit analyses could provide a more compelling case for the adoption of suggested measures.

Seasonal Factors and Carbon Emission Reduction: The study successfully incorporates seasonal variations into the optimization model. However, the manuscript calls for an exploration of large-scale effects, particularly regarding carbon emission reductions. Future work could benefit from a more detailed examination of the macro-scale impacts of proposed conservation strategies on carbon emissions, potentially utilizing scenario analysis to illustrate broader environmental and economic benefits.

Limitations and Future Research: While the manuscript briefly mentions potential improvements and future research directions, a more detailed discussion on limitations, particularly regarding data collection and the quantification of water-saving awareness, would strengthen the study. Future research opportunities, such as exploring socioeconomic, geographical, and climatic factors influencing water and energy use, are crucial areas that could be elaborated further.

Given the manuscript's significant contributions to the field and the outlined areas for improvement, I recommend accepting this study with minor revisions. Addressing the suggested improvements will undoubtedly enhance the manuscript's clarity, depth, and impact. The research provides a valuable foundation for future studies aiming to optimize the water-energy-carbon nexus in urban settings, contributing to the advancement of sustainable urban development practices.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf