Water Quality Improvement through Rainwater Tanks: A Review and Simulation Study

Round 1

Reviewer 1 Report

The manuscript of international team of authors from Australia, Brazil and UAE is concerned with " Water quality benefits through rainwater tanks: a review and simulation study ”.

Thank you for the opportunity to review this timely and useful research study.

The manuscript presents thorough review of water quality data using a rainwater tank, segregating data  as with and without sedimentation. The main result is that measured and simulated data reveal that water collected from the tank is much better than the rainwater directly collected from the roof.

The idea of presented data from different sources showing minimum, maximum and mean values for different water parameters is really very interesting and actual for the water management generally not only in this country.

This submited article could be with the aim and scope of the MDPI journal Water as well as its section: Urban Water Management, https://0-www-mdpi-com.brum.beds.ac.uk/journal/water/sections/Urban_Water_Management and Special Issue: Review Papers of Urban Water Management, https://0-www-mdpi-com.brum.beds.ac.uk/journal/water/special_issues/Urban_Water_2022

• Abstract & introduction: Are focused on the main aim of the paper and what is the new in contribution of authors to the state of art. The abstract with key words very effectively summarize the proposed manuscript.                                                                                          The key objective for authors is to apply progressive simulation tools (not used before for this area). Realistic values are crucial parameters for the accurate design and proper using of stormwater drainage systems.
• Materials & methods: Methods used by authors seems progressive and adequate. This section gives readers enough information so that they can repeat the study for other areas. It is clear how all of the data in the Results section were obtained and the methods used to modeling and analyze the data are scientific sound.                                              To analyse the phenomena through a mathematical model, a hypothetical 5 kL rainwater tank connected with a 200 m2 roof they modelled with the well-establish water quality model, MUSIC (Modelling for Urban Stormwater Improvement Conceptualisation). The simulations were compared with the measured water quality data from a rainwater tank in Melbourne.

With some adaptation this described methodology could be usable more generally not only for selected area of the world.

• Results & discussion: The data are well controlled, robust and results are well presented with relevant and current references. The results show that MUSIC’s simulations on mean daily concentrations of total suspended solids and total phosphorus match with the measured data for Melbourne. Further MUSIC simulations reveal that significant reductions in daily maximum concentrations of total suspended solids; total phosphorus and total nitrogen are expected through a rainwater tank.

Discussion fit with the aims of the study stated in the Introduction. Authors adequately compared their findings with the findings of other studies.

I found the limitations of the study and also the authors write about it - it is not possible to generalise such wide variety of results and the observed generalised relationships of reductions are not expected, as it significantly varies with many other factors such as geography, roof material, proximity to urban activities and rainfall characteristics.

The model was simulated for the rainfall year 1989, why was this 6-minute rainfall for this year selected for modeling?  

• Conclusion: Authors provided useful verification that the effectiveness of rainwater tanks in treating different pollutants through and thorough literature review of measured water quality data and mathematical simulation.
• References: All the references cited are relevant and adequate.

Minor issues for improving of manuscript befor publishing:

• My suggestion for improving this paper or for future research (the weak of the study) is to add more new data set from last years of precipitation for more accurancy in the frame of contemporary climate.
• or more precise describe why selected year is such important as a base for simulations 
• Put units for the equation Nr. 1

Author Response

All the comments are addressed and the manuscript has been revised accordingly.

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper is fairly well written and well referenced. However, the following suggestions may further enhance the quality of this paper:

1. One of the methods used in this study is computing water quality improvement. Why not consider renaming the paper title as “Water quality improvement” instead of “benefits”.
2. The keywords “rainwater tank”, “water quality” duplicate the same in the paper title. Other selections are highly recommended.
3. Is MUSIC considered as a “mathematical model” or a “simulation model” (Line 100)?
4. An English syntax error in Line 134, “has being used”.
5. As the paper title includes “a review”, at least one of the results section sub-headings should use this terminology.
6. A typing error in Table 1, for Greece mean TSS concentration with sedimentation the value is “2.6.00”.
7. Besides, any explanation on why the mean TSS concentration for Sweden is very similar with and without sedimentation?
8. The major flaw of this study is the “material used in constructing the rainwater tank”. Water tank materials greatly affect quality of the stored water. Different countries use different types of tank material. The duration of storage also affects the end results of the stored water. These variations must be clarified in comparing study results from different sources.
9. What is the “rainfall input, a 6-minute rainfall for the year 1989” in Lines 202-203?
10. In the abstract, it is mentioned that MUSIC matches well with measured data. However, in the results section, MUSIC is described as slightly underestimated the measurements. Why?
11. The conclusion section is too lengthy. Some comments have not been described in the study results. Why not restrict it to the significant result findings?
12. This paper also lacks a section in “discussions” of the study results.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The revised manuscript has improved a lot both in results and discussions presentation. Most of my previous comments and suggestions have been adequately addressed. With a thorough proof-check and English-check, this manuscript is readied for publication acceptance.