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Peer-Review Record

Making Rainwater Harvesting a Key Solution for Water Management: The Universality of the Kilimanjaro Concept

Sustainability 2019, 11(20), 5606; https://doi.org/10.3390/su11205606
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Sustainability 2019, 11(20), 5606; https://doi.org/10.3390/su11205606
Received: 8 August 2019 / Revised: 30 September 2019 / Accepted: 2 October 2019 / Published: 11 October 2019

Round 1

Reviewer 1 Report

Strengths of paper: The paper studied a rainwater source from different point of view – I like the historical review of visions from vision of King Parakramabahu of Sri Lanka (12th century) Let no drop of water flow to the sea unused by man; as well as Parkes summarization of the value of rainwater as a source of supply more than one hundred years ago and the suitability of RW for drinking purposes.

The article fills the knowledge gap  about using such alternative water supply systems and their multiply effects for society.

Weakness of paper and suggestion for improvement:

There are necessary further studies and possibility to generalize results for different similar areas. I miss the tables with average values of main contaminants from previous studies. Very briefly is described experiment with AWB artificial roofs.

In row 303 and more is written that for low-income communities, the extended Kilimanjaro Concept should strive for disinfectant free water supply.  Stored water can be intermittently heated (e.g. once per week) to about 80 degrees and kept some 10 minutes at this temperature (pasteurization). Intelligent heating systems can be developed for this purpose, using solar energy or wood from short growth cycle plant species with good calorific  properties – is it the measure against Legionella? Are not these measures too costly?

The collective of authors are very impressive but according my oppinion they were not all included to the paper. I miss some link to the solved project or grant.

 

Author Response

Reviewer 1:

 

Strengths of paper: The paper studied a rainwater source from different point of view – I like the historical review of visions from vision of King Parakramabahu of Sri Lanka (12th century) Let no drop of water flow to the sea unused by man; as well as Parkes summarization of the value of rainwater as a source of supply more than one hundred years ago and the suitability of RW for drinking purposes.

The article fills the knowledge gap about using such alternative water supply systems and their multiply effects for society.

 

Authors’ response:

·         We thank the reviewer for the positive comments, and appreciation of the contribution of our work.

 

Weakness of paper and suggestion for improvement:

There are necessary further studies and possibility to generalize results for different similar areas. I miss the tables with average values of main contaminants from previous studies. Very briefly is described experiment with AWB artificial roofs.

 

Authors’ response:

·         We agree and would like to respond as follows:

(1)   Highlighted that the KC concept through initially developed for Kenya, it can also be extended and adapted to other different areas with similar problems. Specifically we highlighted areas in Asian and South America, where groundwater has high concentrations of toxic geogenic contaminants including arsenic, fluoride and radionuclides.

(2)   Tables with different contaminants have been presented in earlier reviewers including some by the same authors (e.g. Gwenzi et al., 2017). For brevity we avoided reproducing them here, instead we pointed out to the reader that such data exist elsewhere.

 

·         We revised as follows:

 

‘The KC was originally developed to address the problem of high fluoride in groundwater in Kenya. However, due to flexibility and adaptability, scope exist to extend it to other countries in Africa and elsewhere with similar problems. In this regard, the KC can be adapted to regions in Asia and South America, where high concentrations of geogenic contaminants (e.g., As. F. radionuclides) in drinking water pose severe human health risks (Bundschuh et al., 2016).’

 

‘Typical contaminants occurring in rainwater, and the factors influencing rainwater quality are discussed in detail in earlier papers (Gwenzi et al., 2015; Lee et al., 2017). In summary, depending on roof materials, land use, climatic factors and storage conditions, rainwater may contain contaminants such as trace metals, pathogenic organisms, physical objects (e.g. leaves, bird and animal droppings) (Dobrowsky et al., 2014; Gwenzi et al., 2015; Lee et al., 2017).  Thus preliminary analysis, and subsequent treatment using low-cost methods may need to be considered on a case-by-case basis.’

            ‘

In row 303 and more is written that for low-income communities, the extended Kilimanjaro Concept should strive for disinfectant free water supply.  Stored water can be intermittently heated (e.g. once per week) to about 80 degrees and kept some 10 minutes at this temperature (pasteurization). Intelligent heating systems can be developed for this purpose, using solar energy or wood from short growth cycle plant species with good calorific  properties – is it the measure against Legionella? Are not these measures too costly?

 

Authors’ responses:

·         We considered the reviewer’s comments and clarified as follows:

 

‘This is because, chlorination, which is widely recommended by the WHO is not really affordable, and reacts with organic matter in water to form trihalomethanes, which are carcinogenic (Haarhoff et al., 2009).’

 

‘In cases, where contamination of rainwater with pathogenic microbes is expected, suspected, stored water can be intermittently heated (e.g. once per week) to about 80 degrees and kept some 10 minutes at this temperature (pasteurization). In such cases, intelligent heating systems can also be considered for this purpose, using solar energy or wood from short growth cycle plant species with good calorific properties. To avoid excessive costs, such pasteurization should only be applied at local treatment plants to a fraction of the stored rainwater ready for supply. Solar disinfection (SODIS) at individual rural households of quantity sufficient for drinking consumption can be promoted, with better models of SODIS established.’

 

 

The collective of authors are very impressive but according my opinion they were not all included to the paper. I miss some link to the solved project or grant.

 

Authors’ response:

·         We agree to the reviewer’s observation. In fact, we are starting an interesting international collaboration among researchers with diverse expertise drawn from several countries, and this paper is the first one extending the authorship to China (on the Kilimanjaro Concept). QQ, who is basically a linguist played a key role in originating the idea of extending the KC after reading the original paper on the concept. JM is a social scientist involved in the two already published papers on the KC. TBM, a water resources engineer whose PhD was on RWH, she is like the motor of the engine and has been sought for that. CN and WG are senior scientists interested in all aspect of safe drinking water supply. They met RWH in their quest for application of Biochar and Metallic Iron based systems.

·         The concept papers are part of the preliminary work upon which we intend to develop joint research proposals to pilot test the concept ideas.

·         We briefly revised as follows in the Conclusions and Outlook:

‘To demonstrate feasibility of the KC, the next phase of the research should entail pilot-testing the concept at key selected sites’

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Review of Sustainability paper on ‘Kilimanjaro Concept’

This overlong manuscript addresses a water supply technique that the authors call ‘the Kilimanjaro Concept’ (not a term the reviewer has met despite 30 years involvement in East African water supply). Only by the middle of the paper is the ‘concept’ defined - namely as an extension in the scale of practicing rainwater harvesting (RWH).

RWH itself is a long-practiced and extensively reported technique supported by  many governments, NGOs and national RWH associations. The lengthy history and general comments on RWH in the manuscript are rather a distraction from the paper’s purpose and possible contribution. Indeed the paper’s length, and certainly the number of references, could usefully be halved.

Because they makes use of the ground to seasonally store water at no cost, most water supply systems utilise rainfall, that immediately after ‘landing’, has passed into the ground for later retrieval via springs, lakes, streams and wells. Under some circumstances – for example unsuitable geology – it has proved preferable to intercept rainfall before it infiltrates. However this (RWH) requires the construction of expensive water storage tanks/reservoirs and so is most practised under special circumstances such as in semi-arid lands, where effective management for wells is lacking, where aquifers are already seriously depleted etc. Globally the bulk of RWH is roofwater harvesting. However as the roof area per resident x annual rainfall x run-off coefficient rarely exceeds per resident water demand, roofwater harvesting rarely generates a surplus to export from the roofed building. As the ‘Kilimanjaro Concept’ appears to advocate the storage and redistribution of a RWH surplus, it presumably applies primarily to the harvesting of ground runoff flows from steep rocky areas and similar special surfaces. This (limitation) might be made much clearer in the paper.

If we exclude both general/historical observations about RWH and barely suitable roofwater harvesting from it, the paper would most usefully explore the opportunities and limitations of expanding ground-runoff harvesting to a relatively large-scale. Such a scale may require special (e.g. anti-epidemic) water-quality measures - as the paper mentions but too briefly. This paper is not the original generator of the ‘Kilimanjaro Concept’ and so should feature some new analysis about the potential for wide-scale ground-runoff harvesting – especially in regions with over-mineralised aquifers.

For publication in a journal that emphasises 'sustainabily', a discussion of the relative sustainability of respectively decentralised and integrated RWH systems is needed.

Minor point - the Kenya example seems to assume an extremely low water demand - of ca 2 lcd.

Author Response

Reviewer 2:

Review of Sustainability paper on ‘Kilimanjaro Concept’

This overlong manuscript addresses a water supply technique that the authors call ‘the Kilimanjaro Concept’ (not a term the reviewer has met despite 30 years involvement in East African water supply Only by the middle of the paper is the ‘concept’ defined - namely as an extension in the scale of practicing rainwater harvesting (RWH).

Authors’ response:

We considered the comment, and would like to respond as follows:

The Kilimanjaro Concept was introduced in 2018 by the current authors, as solution to the fluorosis crisis the East Africa Rift Valley - this is already highlighted in the Abstract.  This may explain why the reviewer is unfamiliar with the term.

We revised and highlighted the original KC in the Introduction as follows:

‘The Kilimanjaro Concept (KC), is a recent concept developed to address the human health risks associated with high concentrations of fluoride in groundwater in the East African Rift Valley (Marwa et al. 2018, Ndé-Tchoupé et al. 2019). In summary, the original KC entails harvesting rainwater from pristine hilly areas (e.g., Kilimanjaro mountains) and storing it for drinking water supply. Depending on the quality of the rainwater, it can either be supplied directly without treatment or subjected to low-cost treatment in cases of contamination. In some cases, the rainwater can also be blended with groundwater to dilute contaminant to concentrations within the guideline limits for drinking water. ‘

We disagree that the manuscript is overlong – this is 27 pages of double spaced text inclusive of references, which we consider as reasonable for such type of a contribution. Therefore, we made no correction.

RWH itself is a long-practiced and extensively reported technique supported by many governments, NGOs and national RWH associations. The lengthy history and general comments on RWH in the manuscript are rather a distraction from the paper’s purpose and possible contribution. Indeed the paper’s length, and certainly the number of references, could usefully be halved.

Authors’ response:

We have considered the reviewer’s comment. We agree with the reviewer that the history of RWH is very long and rich. We have carefully selected references summarizing the history to first provide a historical background to the reader so that the novelty of our proposed approach (KC), and its extension is clearer. Thus displaying what has already been there and the RWH potential that is yet to be exploited for sustainable water supply. Moreover, we also included this history to illustrate that harnessing rainwater for drinking purposes is not just a localized perspective only for some low-income households or communities, but it is a global view as practiced in India (van Meter et al. 2014) and elsewhere (i.e., the universality of the KC). This is obvious but we are advocating for more than just harvesting and locally use. Even Australia and Germany who are leading in RWH have not yet considered harvesting, infiltrating and use on large scale as one concept in integrated water management. We are not aware on a similar work and we have presented the Indian Perspective (van Meter et al. 2014) in some details. Therefore, in view of the above argument, we made no correction.

Because they makes use of the ground to seasonally store water at no cost, most water supply systems utilise rainfall, that immediately after ‘landing’, has passed into the ground for later retrieval via springs, lakes, streams and wells. Under some circumstances – for example unsuitable geology – it has proved preferable to intercept rainfall before it infiltrates.

Authors’ response:

That rainwater passes into the ground for later retrieval is not true. First, even if it was the case, the reviewer did not consider systematic local infiltration we are advocating for. The ‘side’ effect of avoiding erosion and flooding is also overlooked. We agree with the second point on unsuitable geology. In fact, this point is central to the KC i.e., that where geological conditions are unfavourable (e.g. high geogenic contaminants) intercept the rainwater through rainwater harvesting. We hope the clarifications made earlier on what the KC entails, and what motivated it, and its potential application in other areas in Asia and South America with unfavourable geology address this comment. Therefore, we made no further corrections.

However this (RWH) requires the construction of expensive water storage tanks/reservoirs and so is most practised under special circumstances such as in semi-arid lands, where effective management for wells is lacking, where aquifers are already seriously depleted etc.

Authors’ response:

We have considered the reviewer’s comments and would like to respond as follows:

We are arguing that the technology for this ‘expensive’ tanks is available and locally applicable. The issue of the expensiveness of the technology is questionable and quite relative – we have highlighted cases in Kenya where households and communities have built rainwater storage tanks Moreover, the conditions for the implementations of the KC are ideal in most countries e.g., groundwater with high geogenic contaminants, lack of access to centralized water systems and unreliable drinking water supplies.  

To address the comments we revised by highlighting some of the preconditions for rainwater harvesting, and issues pertaining to sustainability as follows:

‘The initial uptake and adoption of the KC are likely to be rapid and more widespread under certain preconditions, which will also determine the sustainability of the rainwater harvesting systems:

Local need and commitment to harvest rainwater driven by a critical lack of clean drinking water. Examples include; (i) high geogenic contaminants in existing drinking water sources, and (ii) lack of access to decentralized water as is the case in most developing countries. Local positive experience in rainwater harvesting and its benefits, even without the influence of agents such as local extensionists and NGOs. For example, Uganda and in Sri Lanka households are reported to use simple devices such as banana leaves or stems as gutters to harvest up to 200 litres from large tree in a single rain storm (Worm and Hattum, 2006) Frequent failure of traditional drinking water sources such as boreholes, and piped water supply systems due to increasing water demands, and variability of water availability. The potential for rainwater harvesting systems to create co-benefits through multiple uses, including household food production, domestic uses and income generation. Climatic conditions characterized high variability of rainfall, surface and groundwater. In this regard, dry and wet tropical climates with short dry seasons and multiple high-intensity rainstorms may provide ideal conditions for water harvesting. In such cases, rainwater harvesting systems can be used to bridge water shortages during the dry season. Demonstrated technical, financial and socio-economic feasibility, including local technical capacity, community involvement and stakeholder participation including women empowerment.

Globally the bulk of RWH is roofwater harvesting. However as the roof area per resident x annual rainfall x run-off coefficient rarely exceeds per resident water demand, roofwater harvesting rarely generates a surplus to export from the roofed building.

Authors’ response:

We considered the reviewer’s comment and would like to respond as follows:

-The concept presented here goes beyond just the available roof area at household level, to include other catchment surfaces as explained in the manuscript.

-We believe the reviewer reference to total domestic water demand per household include that required for washing, bathing etc. Here, first priority is given to drinking water. The example of AWB in Kenya clearly shows that another perception is possible, also van Meter et al. 2014 or Rai et al. 2019)

Therefore, we made no correction.

As the ‘Kilimanjaro Concept’ appears to advocate the storage and redistribution of a RWH surplus, it presumably applies primarily to the harvesting of ground runoff flows from steep rocky areas and similar special surfaces. This (limitation) might be made much clearer in the paper.

Authors’ response:

We considered the reviewer’s comments, and would like to respond as follows:

-As highlighted already in the paper, clean rainwater should be reserved for drinking purposes.

-Rainwater which may be contaminated may need treatment before use for drinking purposes, while surface runoff can be infiltrated into the ground or used for household food production (the water-food nexus).

We believe this aspects are already highlighted in the paper, thus we made no corrections.

If we exclude both general/historical observations about RWH and barely suitable roofwater harvesting from it, the paper would most usefully explore the opportunities and limitations of expanding ground-runoff harvesting to a relatively large-scale. Such a scale may require special (e.g. anti-epidemic) water-quality measures - as the paper mentions but too briefly.

Authors’ response:

We considered the reviewer’s comments. The concept goes beyond just ground-runoff harvesting to include roofs as catchments. The issue of anti-epidemic water quality measures, have been discussed in an earlier paper on low-cost water treatment systems which form part of the KC. Moreover, examples in Australia and elsewhere show that if water can be keep away from light, oxygen and mosquitoes, no epidemic will occur. In summary, these implementation details are addressed in detail in the paper on the original KC. In the current paper, the statement below, which is already in the manuscript summarizes the point:

‘A key premise of the Kilimanjaro Concept is that rainwater is either free of both pathogens and chemical contaminants, or where pathogens and anthropogenic contaminants exceeding drinking water guidelines occur in harvested RW, they can be removed by simple, affordable and efficient methods like metallic iron (Fe0) amended slow sand filters (Fe0 SSF) (Marwa et al. 2018, Ndé-Tchoupé et al. 2019).’

Therefore, we made no corrections.

This paper is not the original generator of the ‘Kilimanjaro Concept’ and so should feature some new analysis about the potential for wide-scale ground-runoff harvesting – especially in regions with over-mineralised aquifers.

Authors’ response:

We agree, and have lighted in earlier responses that the KC can be extended to Asia and South America where toxic geogenic contaminants occur in groundwater. We also included an analysis on issues pertaining to adoption and sustainability. Therefore, we made no further corrections.

Below are the revisions, which we have already made:

 

‘The KC was originally developed to address the problem of high fluoride in groundwater in Kenya. However, due to flexibility and adaptability, scope exist to extend it to other countries in Africa and elsewhere with similar problems. In this regard, the KC can be adapted to regions in Asia and South America, where high concentrations of geogenic contaminants (e.g., As. F. radionuclides) in drinking water pose severe human health risks (Bundschuh et al., 2016).’

‘The initial uptake and adoption of the KC are likely to be rapid and more widespread under certain preconditions, which will also determine the sustainability of the rainwater harvesting systems:

Local need and commitment to harvest rainwater driven by a critical lack of clean drinking water. Examples include; (i) high geogenic contaminants in existing drinking water sources, and (ii) lack of access to decentralized water as is the case in most developing countries. Local positive experience in rainwater harvesting and its benefits, even without the influence of agents such as local extensionists and NGOs. For example, Uganda and in Sri Lanka households are reported to use simple devices such as banana leaves or stems as gutters to harvest up to 200 litres from large tree in a single rain storm (Worm and Hattum, 2006) Frequent failure of traditional drinking water sources such as boreholes, and piped water supply systems due to increasing water demands, and variability of water availability. The potential for rainwater harvesting systems to create co-benefits through multiple uses, including household food production, domestic uses and income generation. Climatic conditions characterized high variability of rainfall, surface and groundwater. In this regard, dry and wet tropical climates with short dry seasons and multiple high-intensity rainstorms may provide ideal conditions for water harvesting. In such cases, rainwater harvesting systems can be used to bridge water shortages during the dry season. Demonstrated technical, financial and socio-economic feasibility, including local technical capacity, community involvement and stakeholder participation including women empowerment.

For publication in a journal that emphasises 'sustainability', a discussion of the relative sustainability of respectively decentralised and integrated RWH systems is needed.

Authors’ response:

We totally agree and revised by adding the text below:

‘The initial uptake and adoption of the KC are likely to be rapid and more widespread under certain preconditions, which will also determine the sustainability of the rainwater harvesting systems:

Local need and commitment to harvest rainwater driven by a critical lack of clean drinking water. Examples include; (i) high geogenic contaminants in existing drinking water sources, and (ii) lack of access to decentralized water as is the case in most developing countries. Local positive experience in rainwater harvesting and its benefits, even without the influence of agents such as local extensionists and NGOs. For example, Uganda and in Sri Lanka households are reported to use simple devices such as banana leaves or stems as gutters to harvest up to 200 litres from large tree in a single rain storm (Worm and Hattum, 2006) Frequent failure of traditional drinking water sources such as boreholes, and piped water supply systems due to increasing water demands, and variability of water availability. The potential for rainwater harvesting systems to create co-benefits through multiple uses, including household food production, domestic uses and income generation. Climatic conditions characterized high variability of rainfall, surface and groundwater. In this regard, dry and wet tropical climates with short dry seasons and multiple high-intensity rainstorms may provide ideal conditions for water harvesting. In such cases, rainwater harvesting systems can be used to bridge water shortages during the dry season. Demonstrated technical, financial and socio-economic feasibility, including local technical capacity, community involvement and stakeholder participation including women empowerment.

Minor point - the Kenya example seems to assume an extremely low water demand - of ca 2 lcd.

 

Authors’ response:

It is for drinking water only, where the consumption ranges from 2 – 3 lcd. The current trend is to treat only potable water the highest standard. This is sustainable as less chemicals are used.

 

Additional references:

Bundschuh, J., Maity, J.P., Mushtaq, S., Vithanage, M., Seneweera, S., Schneider, J., Bhattacharya, P., Khan, N.I., Hamawand, I., Guilherme, L.R., Reardon-Smith, K., 2017. Medical geology in the framework of the sustainable development goals. Science of the Total Environment.

DOI: 10.1016/j.scitotenv.2016.11.208

Dobrowsky, P.H., De Kwaadsteniet, M., Cloete, T.E., Khan, W., 2014a. Distribution of indigenous bacterial pathogens and potential pathogens associated with roof-harvested rainwater. Appl. Environ. Microbiol. 80 (7), 2307–2316. http://dx.doi.org/10.1128/AEM.04130-13.

Gwenzi W, Dunjana N, C. Pisa, Tauro T and G. Nyamadzawo. 2015. Water quality and public health risks associated with rainwater harvesting systems for potable supply: Review and Perspectives. Sustainability of Water Quality and Ecology, 6: 107-118. http://dx.doi.org/10.1016/j.swaqe.2015.01.006

Haarhoff, J., et al., 2009. NOM characterization and removal at six Southern African water treatment plants. Drink. Water Eng. Sci. Discuss. 2, 231e257.

Lee M., Kim M., Kim, Y., Han, M. (2017). Consideration of rainwater quality parameters for drinking purposes: A case study in rural Vietnam. Journal of Environmental Management 200: 400 – 406.

Worm J, van Hattum T. 2006. Rainwater harvesting for domestic use. Agrodoc 43. Agromisa Foundation/CTA, Wageningen.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Please, see attached.

 

Comments for author File: Comments.pdf

Author Response

Authors’ Responses to Referee’s Comments on 2nd revision to Manuscript “sustainability-580638” about ‘Kilimanjaro Concept’ – September 2019

 

After reading the authors’ response to his criticism of earlier drafts, it is now clear to this reviewer that his ideas as to what are a suitable style, content and length of a published technical paper are largely at variance with the ideas of the authors. So further ‘correspondence’ about its form serves no purpose.

 

Authors’ response:

We agree that we disagreed the earlier reviewer’s comments, and provided a detailed rebuttal justifying our position. However, we have shortened and summarized one of the quotes on the history of RWH to:

‘In the late 1880, Parkes [16] summarized the value of rainwater as a source of supply as follows: (1) its general purity and great aeration make it both healthy and pleasant, (2) the greatest benefits occur when rainwater is used for drinking water supply instead of spring or well water, which is often largely impregnated with salts, and (3) in cases of cholera, rainwater is less likely to become contaminated with sewage than wells or springs’

We noted that in the previous revision we compared the Kilimanjaro Concept to the current practices of drinking water supply based on groundwater (Section 3.6), and included a Table 1 summarizing the novelty of the KC. However, the current version of the manuscript on the journal website does not have this material, and the reason for this is unclear to us. A possibility exists that an earlier version rather than the revised version of the manuscript was sent to the reviewer. This is particularly so given that the revision dossier was submitted via e-mail because the journal online system did not provide an option to submission a revision – we indicated this to the journal contact person responsible for handling the manuscript. Yet some of the reviewer’s comments are addressed in this text. Therefore, we revised to include the omitted text (Section 3.6) and Table 1), and highlighted the text in the attached manuscript with track changes.

 

The paper – as the authors insist – is about a concept, or to use a less favourable word about an assertion. The concept, as I understand them, is that although rainwater harvesting (both domestic supply and for irrigation) is has generally been practiced on a small spatial scale over many centuries, under circumstances such as the over-mineralisation of groundwater it might economically be practiced on a large scale. That might entail interception of surface run-off, pumping to reservoirs and subsequent gravity-powered distribution by pipe. Some little experience in East Africa, mainly using rock-face run-off, is offered as a possible model for practice in particular parts of China.

 

Authors’ response:

We agree with the reviewer’s comment that this paper is about a concept. To further emphasize that this is a concept rather than an assertion, and that it has not be subjected to field implementation and evaluation, we have included the term ‘potential’ in the text. To further indicate that our concept is consistent with other recent studies, we included the following references and cited them as follows:

‘Recently, some studies have investigated the following: (1) surface treatments for enhancing rainwater harvesting [30], (2) site selection for rainwater harvesting and subsequent storage systems [32], and (3) the effects of climate change and variability on urban rainwater harvesting systems [33]. These recent studies provide critical information for the implementation of the Kilimanjaro Concept.’

 

Hussain, F.; Hussain, R.; Wu, R.-S.; Abbas, T. Rainwater harvesting potential and utilization for artificial recharge of groundwater using recharge wells. Processes 2019, 7, 623.

Hamilton, K., Reyneke, B., Waso, M., Clements, T., Ndlovu, T., Khan, W., DiGiovanni, K., Rakestraw, E., Montalto, F., Haas, C.N., Ahmed, W., 2019. A global review of the microbiological quality and potential health risks associated with roof-harvested rainwater tanks. Journal of Clean Water, https://doi.org/10.1038/s41545-019-0030-5

Ibrahim, G.R.F.; Rasul, A.; Ali Hamid, A.; Ali, Z.F.; Dewana, A.A. Suitable site selection for rainwater harvesting and storage: Case study using Dohuk Governorate. Water 2019, 11, 864.

Kisakye, V.; Van der Bruggen, B. The viability of artificial surface treatments as a mechanism for domestic rain water harvesting. Phys. Chem. Earth 2018, 107, 8–18.

Zhang, S.; Zhang, J.; Yue, T.; Jing, X. Impacts of climate change on urban rainwater harvesting systems. Sci. Tot. Environ. 2019, 665, 262–274.

 

About 20% of the paper comprises excerpts from the history of rainwater harvesting, but which do not support any discussion of the best size for units of its practice. To my mind that part of the paper contributes nothing new to the history of the technique (or to historiography) nor provides any new critique of its scale of practice. The widely used and rather charming Sri Lankan quote doesn’t particularly or even mainly relate to RWH.

Authors’ response:

We considered the reviewer’s comment and shortened and rephrased one of the statement on the history of RWH as follows:

‘In the late 1880, Parkes [16] summarized the value of rainwater as a source of supply as follows: (1) its general purity and great aeration make it both healthy and pleasant, (2) the greatest benefits occur when rainwater is used for drinking water supply instead of spring or well water, which is often largely impregnated with salts, and (3) in cases of cholera, rainwater is less likely to become contaminated with sewage than wells or springs’

RWH focusses on using rainwater where and when it falls, which is consistent with the statement that, ‘Let no drop of water flow to the sea unused by man’, when can be loosely interpreted to mean that, ‘harvest and use all rainwater before it flows to the sea.’ We fail to understand why the reviewer thinks that this statement is not related to RWH. Therefore we retained the statement. The text on the history of RWH (i.e., from Parkes [16] and Sri Lanka) only constitutes circa 169 words of the total 7683 words of the main text. This is equivalent to just circa 2% of the length of the manuscript, yet the reviewer claims that this constitute 20%. The reason for the 10 times exaggeration is unclear to us. However, as highlighted above, we have shortened the text from Parkes [16] to just 76 words. The detailed designs including optimum sizes of storage can only be determined during the detailed design phase not at concept level. Thus we revised the Conclusion and Outlook to include the statement:

‘Such pilot studies should include detailed design and analysis, and socio-economic and financial evaluation of the concept versus other competing options such as centralized drinking water systems and groundwater-based water supply systems.’

 

The definition of the term ‘rainwater harvesting’ is somewhat contentious but there seems general agreement that it describes the interception of SURFACE runoff following rainfall. The surface might be roofs, lightly-vegetated sloping ground, roads etc. This also appears to be the authors’ understanding and – as elsewhere - they consider RWH as especially applicable in locations where groundwater is highly mineralised. RWH unfortunately involves high water-storage costs, especially in locations where rainfall is very seasonal – as in Africa except for a narrow equatorial band and in almost all of China. This sets the context in which any extension or variation of RWH might be set and is indeed the context chosen by the authors.

 

Authors’ response:

A summary description of what RWH and the KC entails is provided in the text, including the nature of ideal catchment areas. In the previous revision we compared the Kilimanjaro Concept to the current practices of drinking water supply based on groundwater (Section 3.6), and included a Table 1 summarizing the novelty of the KC. However, the current version of the manuscript on the journal website does not have this material, and the reason for this is unclear to us. A possibility exists that an earlier version rather than the revised version of the manuscript was sent to the reviewer. This is particularly so given that the revision dossier was submitted via e-mail because the journal online system did not provide an option to submission a revision – we indicated this to the journal contact person responsible for handling the manuscript. Yet some of the reviewer’s comments are addressed in this text. Therefore, we revised to include the omitted text (Section 3.6) and Table 1), and highlighted the text in the attached manuscript with track changes.

 

I do not feel the paper incudes either theoretical/economic analysis or reports of field practice to convert an assertion (about large-scaled RWH) that might justify its wider acceptance as a potentially important concept.

 

Authors’ response:

As a concept, it should be noted that economic analysis of the KC concept cannot be done at concept level, but rather during detailed design and analysis on a case-by-case basis as already highlighted in the manuscript. The theoretical concept is the extension of the KC and its associated benefits relative to conventional drinking water supply based on borehole drilling. Table 1 in the manuscript summarizes this aspect. We have also highlighted that besides Africa, several places in Asia and Latin America have the problem of toxic geogenic contaminants in groundwater, thus making RWH the potential source of drinking water (See Section 3.6). In the previous revision we compared the Kilimanjaro Concept to the current practices of drinking water supply based on groundwater (Section 3.6), and included a Table 1 summarizing the novelty of the KC. However, it seems the version submitted to the reviewer was an older one which did not address the aspects. Thus we revised by including Section 3.6 and table 1 comparing the Kilimanjaro Concept to the current approach to clean water provision based on borehole drilling. Detailed economic analysis can only be done during the detailed design phase not at concept level. We revised the Conclusion and Outlook to emphasize this point as follows:

‘Such pilot studies should include detailed design and analysis, and socio-economic and financial evaluation of the concept versus other competing options such as centralized drinking water systems and groundwater-based water supply systems.’

 

So I find this manuscript rather a missed opportunity to explore a possibly important variant of RWH. The authors’ keenness to defend its present style, length and content indicates little scope for significantly amending the manuscript. I therefore continue not to recommend publication, but the publisher must choose how to proceed (i.e. whose ‘side’ to take).

Authors’ response:

We considered the reviewer’s comments, and respond as follows: Shortened and rephrased some of the text on history of RWH We fail to understand how a manuscript with a main text of just 10 pages can be considered as long. In fact we had to include more text in an effort to address the reviewer’s comments.

 

In summary, we feel we have attempted to the best of our ability to address the reviewer’s comments, and where we differed with the reviewer’s opinion, we have provided a justification for our rebuttal.

Author Response File: Author Response.docx

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