Round 1

Reviewer 1 Report

a nice piece of work on AL

more link to work already published on relative subjects regarding RL is needed

see some indicative suggestions in the annotated manuscript attached 

Comments for author File: Comments.pdf

Author Response

A nice piece of work on AL

Thank you.

More link to work already published on relative subjects regarding RL is needed.

More references related to Real Losses have been added to the manuscript.

See some indicative suggestions in the annotated manuscript attached.

Corrected.

Reviewer 2 Report

The paper aims to propose a standard procedure to determine the optimum tradeoff between the marginal cost a water utility bears to implement activities aimed at reducing apparent losses (i.e., meter replacement and frequent connection inspection), and the marginal benefit consequently achieved. The authors see a gap in the literature on apparent water losses and claim that no standard terminology, performance indicators, and methodology to quantify the various components of apparent losses have been proposed, in contrast with the IWA practices that regard real water losses. To address this research gap, the contribution of the paper consists in (i) classifying and defining the different components of apparent water losses, (ii) proposing a simplified methodology to obtain the optimal intervention frequency and evaluate the so-called “Economic Level of Apparent Losses”, and (iii) proposing a set of performance indicators to evaluate apparent losses. The proposed methodology is then showcased in two fictitious examples in the Appendix of the paper.

While the paper is relevant in the literature and is methodologically sound, I think that its quality should be improved with respect to two major aspects that I suggest to revise:

·      First, an application of the proposed methodology to a real case study with data from a sample utility would definitely add value to the proposed methodology and serve as an example for other water utilities.

·      Second, it looks to me that some of the quantities included in the methodology can be very uncertain to estimate and hard to observe accurately (e.g., the cost of illegal connections, the meter failure frequency, etc.). Thus, a sensitivity analysis showing how the results change when varying the various input values is needed to understand how reliable it is to inform water utilities’ strategies.

 

OTHER COMMENTS BY SECTION

INTRODUCTION

·       Lines 38-39: please support with references and, possibly, real-world examples with costs.

·       Sentence in lines 53-54 is very generic and confused. Please be more specific. What do you mean by “general perspective”, “partial way”, specific issues”?

·       Lines 82-85: who is proposing this categorization? Please clarify whether you are proposing this, or report a reference if not.

COMPONENT OF APPARENT LOSSES

·      Line 242-243. Please support with references.

 

OTHER MINOR COMMENTS

·      Line 87: correct “does to take” with “does not take”.

·      Line 104: correct “correspond” with “corresponds”.

Author Response

The paper aims to propose a standard procedure to determine the optimum tradeoff between the marginal cost a water utility bears to implement activities aimed at reducing apparent losses (i.e., meter replacement and frequent connection inspection), and the marginal benefit consequently achieved. The authors see a gap in the literature on apparent water losses and claim that no standard terminology, performance indicators, and methodology to quantify the various components of apparent losses have been proposed, in contrast with the IWA practices that regard real water losses. To address this research gap, the contribution of the paper consists in (i) classifying and defining the different components of apparent water losses, (ii) proposing a simplified methodology to obtain the optimal intervention frequency and evaluate the so-called “Economic Level of Apparent Losses”, and (iii) proposing a set of performance indicators to evaluate apparent losses. The proposed methodology is then showcased in two fictitious examples in the Appendix of the paper.

While the paper is relevant in the literature and is methodologically sound, I think that its quality should be improved with respect to two major aspects that I suggest to revise:

•               First, an application of the proposed methodology to a real case study with data from a sample utility would definitely add value to the proposed methodology and serve as an example for other water utilities.

We agree with the reviewer that a complete real case study could be useful for the readers. In fact, the second case study in the appendixes already uses real data from a medium size water utility in the East coast of Spain. However, we have reduced the number of different types of meters and customers to make it easier to follow. In any case, it is also true that a complete real case study could become extremely complex and long because of the number of different types of meters and customers.

Finally, we would like to emphasise that the main purpose of the paper is to present the general methodology on how the ELAL could be calculated. Consequently, our aim due to obvious reasons related to the limited length of a research paper, is not to provide details on the specific methodologies that need to be applied to obtain the parameters required to calculate the ELAL but to describe the general methodology.

For all of the above, we believe that the second case study presented already meet the request made by the reviewer and can serve as a reference for water utilities on how to apply the proposed methodology. However, as mentioned in the following answer to the reviewer we have added a sensitivity analysis to the case study.

•               Second, it looks to me that some of the quantities included in the methodology can be very uncertain to estimate and hard to observe accurately (e.g., the cost of illegal connections, the meter failure frequency, etc.). Thus, a sensitivity analysis showing how the results change when varying the various input values is needed to understand how reliable it is to inform water utilities’ strategies.

A sensitivity analysis on how the different parameters affect the final value of ELAL has been conducted and added to the second case study. The variables explored are those for which some uncertainty in their determination may exist, namely ADR and AICR.

As it can be seen in the sensitivity analysis, the most important parameters that affect the ELAL are related to water meter inaccuracies (ADR), as this term is of larger magnitude than the one referred to illegal uses (AICR). Also, and because the driving variables are affected by a square root, the sensitivity of these variables on the final the result is drastically minimized. For example, an error in the estimation of the ADR of the largest group of meters (domestic meters) of 50% will only cause an error of estimation of the ELAL of approximately 5%.

 

OTHER COMMENTS BY SECTION

INTRODUCTION

•       Lines 38-39: please support with references and, possibly, real-world examples with costs.

Several references have been added to the text. However, in the authors’ opinion, adding examples of costs does not contribute to emphasise the importance of apparent losses. Each water utility is different and the proportion between real and apparent losses in terms of volume/cost will differ from one place to another. The reference Kingdom et al. 2006 (a report from the World Bank) includes several tables with the proportions of RL and AL for different regions in the world. This reference has been added to the manuscript.

(SEE DOCUMENT ATTACHED)

 

•       Sentence in lines 53-54 is very generic and confused. Please be more specific. What do you mean by “general perspective”, “partial way”, specific issues”?

Sentence has been rewritten.

•       Lines 82-85: who is proposing this categorization? Please clarify whether you are proposing this, or report a reference if not.

This categorization is an original contribution in the manuscript. We have modified the sentence to better clarify that the new categories are proposed by the authors in order to be able to conduct the calculation of the ELAL.

 

COMPONENT OF APPARENT LOSSES

•      Line 242-243. Please support with references.

Data handling errors are caused by an improper manipulation of water meter readings and/or the calculation procedures used to estimate water consumption when readings are not available. Therefore, as long as the calculation procedures are not modified in the water utility, the magnitude of these errors will remain more of less constant and will not experience a significant change. In fact, the book by Thornton et al. (2008) chapter 14, is entitled “Controlling Apparent Losses from Systematic Data Handling Errors in Customer Billing Systems”. In other words, the authors assume that data handling errors are systematic and, therefore, will be constant unless the internal water consumption calculation procedures and data handling by the water company changes.

The following reference has been added:

Julian Thornton; Reinhard Sturm; George Kunkel: Water Loss Control, Second Edition. Controlling apparent losses from systematic data handling errors in customer billing systems, Chapter 14 (McGraw-Hill Professional, 2008 2002), Access Engineering

 

OTHER MINOR COMMENTS

•      Line 87: correct “does to take” with “does not take”.

Corrected

•      Line 104: correct “correspond” with “corresponds”.

Corrected

Author Response File: Author Response.docx

Reviewer 3 Report

Introduction

The paper is about presenting a methodology to reduce the leakage (apparent and real losses) in a system which is interesting, however, not really new! The paper is poorly structured and does not seem to be reviewed by a native speaker to fix the grammatical errors and inappropriate word selections. Where is the case study in this paper? Where is the results section? Where is the discussions of practical implications? You have not proved the superiority of your method in a case study and through discussions of it? Why would I buy it? The paper is incomplete and I am afraid, I’d have to say the papers in this shape in nowhere close to being published, unless the authors make major changes and resubmit.

General Comments:

Please re-write the abstract. It says nothing but methodology and introduction. The abstract needs to be about the summary of what was done and what was achieved, the advantages of the study, the novelties and in short why someone needs to read this paper.

Lines 62-66: Are the most important messages and set the tone for the rest of the paper, but it is not clear. Sounds like a run-on sentence. Please reword.

Throughout the paper, the authors make mention of optimizing the leakage, however, no optimization algorithm is introduced to prove this claim. Note, you can only use the term optimization, only and only if you have used optimization algorithms, otherwise you are only “improving” the leakage and not “optimizing”. Please revise.

A lot of discussions throughout the “Introduction” are only story telling as they are not backed up by proper citations. Either add citations or just simply throw them out. Everybody knows that aging eater meters include errors I recording data.

Specific Comments:

Caption of Figure 1, needs reference

Line 49, what do you mean by “eminently practical”? Please rephrase.

Line 55, have managed to standardize

Lines 57, 58: are these stats (30 and 50%) universal or in Spain? Please clarify.

 Line 444, …this figures… lease use these.

Line 448, …also, an in order to…. Rephrase.

Line 450, why is this one statement a separate paragraph?

Line 452, use smaller letters for authors

 

Author Response

INTRODUCTION

The paper is about presenting a methodology to reduce the leakage (apparent and real losses) in a system which is interesting, however, not really new!

The paper only deals with apparent losses. It does not pretend to describe a methodology to reduce water losses in a system. The manuscript presents a calculation proposal to estimate the optimum level of apparent losses which has not been published yet.

The paper is poorly structured and does not seem to be reviewed by a native speaker to fix the grammatical errors and inappropriate word selections.

We have put a lot of effort in trying to present the concepts and calculation procedures in the best possible manner and to submit a properly structured manuscript. In fact, three of the authors are associate editors of several research journals and we are perfectly aware of the importance of submitting a properly structured manuscript.

The manuscript was revised in its first version by a native speaker. We have corrected some sentences and some grammatical errors as advised by other reviewers.

Where is the case study in this paper?

The two case studies were detailed in the appendixes of the manuscript. In our opinion, including the case studies within the main body of the manuscript would have made it too long. By adding the case studies as separate appendixes we could include two of them (one simplified and a second one with more details), and keep the methodology alone in the main body.

Where is the results section? Where is the discussions of practical implications? You have not proved the superiority of your method in a case study and through discussions of it? Why would I buy it? The paper is incomplete and I am afraid, I’d have to say the papers in this shape in nowhere close to being published, unless the authors make major changes and resubmit.

Instead of adding a discussion section within the main body, it was decided to present and discuss the results at the end of each case study to facilitate the understanding of the methodology.

Our methodology does not pretend to be superior to any other methodology: the paper describes a calculation proposal for the optimum level of apparent losses. Contrary to what is available for real losses, there is no alternative proposal in technical literature on how to estimate the economic level of apparent losses (and this is the main contribution of the work).

 

 

GENERAL COMMENTS

Please re-write the abstract. It says nothing but methodology and introduction. The abstract needs to be about the summary of what was done and what was achieved, the advantages of the study, the novelties and in short why someone needs to read this paper.

The abstract has been completely rewritten following the reviewer comment.

Lines 62-66: Are the most important messages and set the tone for the rest of the paper, but it is not clear. Sounds like a run-on sentence. Please reword.

The sentence has been modified.

Throughout the paper, the authors make mention of optimizing the leakage, however, no optimization algorithm is introduced to prove this claim. Note, you can only use the term optimization, only and only if you have used optimization algorithms, otherwise you are only “improving” the leakage and not “optimizing”. Please revise.

The paper deals with a methodology to calculate the optimum level of apparent losses (which is not the same as leakage or physical losses). As the reviewer knows, in a cost function that depends on several variables the optimum corresponds to that combination of the parameters that provide the least cost (minimum of the function). In this case, the paper proposes a method to build the cost function of apparent losses considering the accepted IWA components and the costs involved. These costs are basically the cost of the water losses and the cost of implementing water losses reduction measures (water meter replacement + customers’ connections inspection). The optimum is obtained at the minimum of the cost function. The minimum of the function is obtained by calculating the derivative of the function and equating it to zero. No optimization algorithm is needed for this.  The simplicity of the cost function makes it possible to find an analytical solution.

A lot of discussions throughout the “Introduction” are only story telling as they are not backed up by proper citations. Either add citations or just simply throw them out. Everybody knows that aging water meters include errors I recording data.

More citations have been added in the introduction section. In any case, it should be mentioned that, in the first version, the introduction section already had 23 references.

Specific Comments:

Caption of Figure 1, needs reference

A reference has been added.

Line 49, what do you mean by “eminently practical”? Please rephrase.

The sentence has been re-written.

Line 55, have managed to standardize

Corrected.

Lines 57, 58: are these stats (30 and 50%) universal or in Spain? Please clarify.

As supported by the references used (3 and 16) these general figures are international references which can significantly vary depending on the tariff. For that reason we use the formula “…can reach up to…”

The reference Kingdom et al. 2006 (a report from the World Bank) include several tables with the proportions of RL and AL for different regions in the world. This reference has been added to the manuscript.

(see figures in document attached)

 

Line 444, …this figures… lease use these.

Corrected.

Line 448, …also, an in order to…. Rephrase.

Corrected.

Line 450, why is this one statement a separate paragraph?

Paragraphs have been merged together.

Line 452, use smaller letters for authors

Corrected.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper has been improved. It still needs though further improvement regarding the English. 

As the core idea is the AL the paper should include a comparative analysis of its approach vs the one applied for RL

Comments for author File: Comments.pdf

Author Response

The paper has been improved. It still needs though further improvement regarding the English.

Further changes have been introduced to improve English language. A native English editor has reviewed the grammar and language style.

 

As the core idea is the AL the paper should include a comparative analysis of its approach vs the one applied for RL

Thank you for the suggestion. A new Appendix has been added to the manuscript. This appendix includes a table with the comparison of the variables used for the calculation of the economic level of real losses against the ones used for apparent losses.

Reviewer 2 Report

The paper has been improved and suitable changes have been implemented to address my comments. I only suggest to further improve it according to the following two minor suggestions:

·      I would mention a few sample results from the second case study (and its sensitivity analysis) already in the main body of the paper, in order to showcase which kind of output recommendation can be obtained by adopting the proposed methodology. A couple of sentences that summarize the conclusions of the second case study can be enough, given that details are all given in the Appendix.

·      When presenting the second case study, the authors state that “The data used in this case study has been partially taken from a medium size water utility in Spain”. I encourage them to provide more specific information on the considered case study in terms of (i) name of the city/town, (ii) name of the utility, (iii) description of the case study in terms of number of users served and number of meters deployed.

Author Response

The paper has been improved and suitable changes have been implemented to address my comments. I only suggest to further improve it according to the following two minor suggestions:

·      I would mention a few sample results from the second case study (and its sensitivity analysis) already in the main body of the paper, in order to showcase which kind of output recommendation can be obtained by adopting the proposed methodology. A couple of sentences that summarize the conclusions of the second case study can be enough, given that details are all given in the Appendix.

Following the recommendation of reviewer 2 comments about the case study have been added to the main body of the manuscript.

 

·      When presenting the second case study, the authors state that “The data used in this case study has been partially taken from a medium size water utility in Spain”. I encourage them to provide more specific information on the considered case study in terms of (i) name of the city/town, (ii) name of the utility, (iii) description of the case study in terms of number of users served and number of meters deployed.

Additional information has been added to the introduction of the second case study.

The information about the meter degradation rate was partially taken from a PhD research conducted by Francesc Gavara in Castellon de la Plana (The research can be downloaded from the following URL https://riunet.upv.es/handle/10251/62182). The city has a population of approximately 175.000 citizens and the number of connections is closed to 50,000.

The utility operating in Castellon de la Plana is FACSA (https://www.facsa.com/).

We have preferred not to mention the specific city for several reasons:

-          Confidentiality. The Water utility is not kin in having the name of the city published

-          In reality, the case study is based on the results obtained about the meter degradation of two meters used by this utility.  However, there are other brands of meters that are also used at this time. Therefore, the actual economic level of apparent losses will be slightly different than the one obtained and the calculation will become more complex.

-          The idea of the case study was to show how the proposed calculation methodology could be applied, not to provide reference values for the economic level of apparent losses.

Reviewer 3 Report

I recommend that the authors avoid using the term "optimization: anywhere in the paper, if they have not actually used optimization algorithms, as this is not common in scientific articles to do so. 

Author Response

 I recommend that the authors avoid using the term "optimization: anywhere in the paper, if they have not actually used optimization algorithms, as this is not common in scientific articles to do so.

When possible, the words “optimization” and “optimized” have been removed from the manuscript and substituted by the words “minimization”, “minimized”, or “economic level”