Differences in Microbial Communities in Drinking Water from Conventional Electronic and Manual Taps in Dependence on Stagnation and Flushing Cycles

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Dear Athors, as I alredy mentioned CFU determination is no adequate method for studying microbial load or bacterial contamination.

The investigations are on bachelor thesis level and not for publishing in a scientific journal.

Author Response

Dear Reviewer,
Thank you very much for your work. Unfortunately, it is not possible for us to change the study design and use other parameters than CFU for an evaluation.

Kind regards,
Anja Knecht

Author Response File: Author Response.docx

Reviewer 2 Report (Previous Reviewer 1)

Based on my previous comments, i see that authors have addressed my comments therefore i approve this paper 

Author Response

Dear Reviewer 2,

Thank you very much for your work and approving out article for MDPI water.

Kind regards,

Anja Knecht

Reviewer 3 Report (New Reviewer)

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 3, 

Thank you very much for your work! You can find our Point-to-Point Response in the attached file.

Kind regards,

Anja Knecht

Author Response File: Author Response.docx

Reviewer 4 Report (New Reviewer)

In this work, the authors invetigate the water quality from different types of taps. The topic is interesting and the data are sufficient for this stdy. But there are some issues need to be addressed before being accepted.

-In Figure 1, it is better to indicate the difference between E1 and E2 because from the image, there is no obvious difference. 

-In Figure 2, the red lines to indicate the grammar mistakes are still left there. 

-Sometimes, there is space between "15 °C", sometimes there is not like "15°C". Please make them uniform.

- Sometimes, the liter is expressed as "L" but sometimes is expressed as "l" in "ml". It is better to correct ml into mL.

Author Response

Dear Reviewer,

many thanks for your work, you can find our Point-to-Point-Response in the attached file.

Kind regards,

Anja Knecht

Author Response File: Author Response.docx

Reviewer 5 Report (New Reviewer)

This paper investigates the impact of tap design and functionality on the microbial growth and risk, assessed by coliform bacteria, P aeruginosa, and L pneumophila. The outset of the study is mostly clear, and the experimental design appear to be robust. The authors build their study on previous literature and manage to present results in a overall clear understandable way.

However, there are some concerns:

1. When electronic vs manual taps are discussed, it seems that the conclusion is that stagnant volume and longer stagnation times are mainly responsible for microbial load/risk. However, in the paper you do not clearly state the stagnant volumes (or surface-to-volume-ratios) for the taps investigated. The explanatory significance of this parameter ought to be high.

2. The statement on line 403 and 404 beginning with "More CFUs are found in...", but the results do not seem to support this statement very strongly. In setup A there's no statistically significant difference between taps, and in setup B it appears we only see that longer stagnant times result in higher CFU. What is the statement based on? A clarification would be helpful for the reader.

3. The conclusion seems to be that electronic or manual tap has no significance, but rather stagnant volume and stagnant time. This could be stated/shown more clearly, since this is one of the more interesting findings.

Some minor observations:

Line 35: the 6 in 106 should be superscript.

Line 379 pp: In this paragraph there are some repetetive phrasing: "For some years now", "for several decades now" and "...mounting for some years". While of little significance to the quality of the results, it might enhance the impression of the paper if this paragraph were revisited.

Author Response

Dear Reviewer,

thank you very much for your work. You can find our response to your comments in the attached file.

Kind regards,

Anja Knecht

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report (Previous Reviewer 3)

Dear authors

as already mentioned, CFU determination is not a sufficient and up-to-date method to determine the microbial load in any habitat. It does not represent the total amount of microorganisms; dead cells, VBNC, damaged cells are neglected.  CFU only estimates the number of viable and cultivable cell of the specific used media. Especially drinking water, as an extreme and oligotrophic habitat, harbors many cells which occur as persiter-cells or complete starvation to metabolically adapt to this oligotrophic environment. It is also known, that the VBNC state or starvation processes of pathogenic organisms can be induced by tap water and these bacteria fail to grow on routine bacteriological media. However, they are still alive by low levels of metabolic activity. Therefore, being aware of these facts, it is nowadays mandatory to apply a polyphasic approach by “modern” microbial- and molecular methods to investigate “microbial risk” in any habitat. Using only cultivation techniques is not contemporary and appears as a step backwards into the 50^th and the work is not proficient.

I know that the study design cannot be changed anymore, however, it should be of good scientific practice to think about an appropriate and well organized study design before starting an experiment. Here, it seems, as this has not been done prior to the experiment and to publish the presented results, additional experiments are still needed. Therefore, I recommend to reject this manuscript.

Author Response

Dear Reviewer,

We are sorry, that you are not happy with our work!

Kind regards,

Anja Knecht

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Reviewer 2 Report

On the whole, I see the article as very interesting since it deals with an important subject regarding the quality of drinking water at the recipient. This study aims to investigate the impact of the microbial quality of drinking water varies for different types of faucets and under different flushing conditions. The aim is clear.

I found all methodologies adopted well-conducted and described with all the needed monitoring parameters. However, for easier perception, I propose dividing the methodology description into separate sections - construction of the test installation, sampling, and microbiological analyses.

The results and discussion have been described well, but sometimes require a few minor corrections and intervention. The same descriptions above Figures 3 (a) and (b) are misleading. Searching for an explanation in the descriptions below the figure is troublesome. In the discussion of the titles of subsections 4.2. and 4.3, excessive punctuation should be removed. The required statistical analysis has been well conducted.

Thus, I recommend for publication this work with minor corrections.

This work would have been better supported and associated with studies of the abundance of biofilm in the taps. Even so, it is now far too late to do so in this study. I encourage the authors to do this in similar future work.

Reviewer 3 Report

Dear Authors,

The manuscript entitled “Microbial contamination in conventional electronic and manual water taps: investigating critical parameters that influence microbial contamination of drinking water” is of great interest for the readers and fits to the scope of this journal. It deals with the “bacterial contamination” of drinking water. The authors used traditional cultivation techniques for their investigations according to the European Drinking Water Directive.

However, determination of CFU does not represent “bacterial contamination”. If the authors are talking about bacterial contamination, other up-to-date methods to study bacterial communities have to been used. Bacterial communities are not represented by the small amount of the cultivatable fraction (mostly under 1%) of the whole consortium inhabiting water systems. Therefore, the manuscript should be revised by applying methods for studying the whole bacterial community. This would provide a scientific overview of effects of parameters that influence microbial contamination in tap water systems.

The manuscript contains all elements of a scientific paper. 

The abstract gives a short summary of the used methods, results and conclusion.

The introduction part provides a good overview of the importance of the topic. The literature is up to date and comprehensive.

Within the Material and Methods part, the authors described the sampling and used methods in detail. This part of the manuscript is well structured, and can easily be followed.

The Results part is well structured and contains all results, which are clearly displayed in tables and figures.

Discussion part contains all results, however it is very short and does not correspond to the title of the manuscript (bacterial contamination cannot be investigated by CFU measurement