Assessing SDG indicator 6.4.2 ‘level of water stress’ at major basins level

This is a very interesting study. I enjoyed reading the manuscript. Nevertheless, it needs some further improvements. In general, there are still some occasional grammar errors throughout the manuscript, especially the article "the," "a," and "an" is missing in many places; please make a spellchecking in addition to these minor issues. The reviewer has listed some specific comments that might help the authors further enhance the manuscript's quality.

1. Specific Comments

A list of acronyms is needed.

• Introduction
• The objectives should be more explicitly stated.
• What is the novelty of this work?
• Methods
• All variables should be explained.
• Results
• This section is well written.
• Discussion
• The discussion should summarize the manuscript's main finding(s) in the context of the broader scientific literature and address any limitations of the study or results that conflict with other published work.

The authors provide a realistic, implementable methodology to make the SDG6 water stress indicator at the river basin level, and use their methodology to demonstrate the state of the indicator using verified, globally applicable data sets that are maintained in FAO's AQUASTAT. I expect this paper to be extensively used by researchers, professionals and countries and to set a standard in the assessment and collaborative, holistic management of river basins.

This paper presents an interesting technical method to disaggregate the indicator 6.4.2. I found the paper to be overly technical and didn’t bring forth the importance of accurately monitoring and measuring the indicator. The paper could benefit from highlight real-life examples where levels of water stress at major basins have caused human and environmental suffering. I also think the paper missed an opportunity to highlight issues of data collection at country level on the indicator. While the methodology is important in monitoring the indicator, ensuring that accurate and reliable data is collected at national level is critical. I didn’t get a sense of whether the authors found this to be a challenge that would ultimately hinder the ability to report on the indicator. Furthermore, I believe the paper could have benefited from zooming in onto a specific context to demonstrate how robust the indicator is in assessing the indicator at regional and subregional levels.

Other important comments: there are grammatic errors that need to be addressed all through the paper which make it difficult to read.

For none technical readers the paper might be a little confusing if the methods and formulars are not explicitly explained.

The results section is clear and reads well. In fact, it allows practitioners to understand issues related to indicator 6.4.2 and the implications of measuring or not measuring this indicator at national level. However, I do feel that you can expand a little bit on population densities as playing a significant role in increasing water stress. Although mentioned on the last paragraph of the results section, it might be beneficial to expand on this a little further and perhaps engage with how the method would, in future, need to take into consideration population densities as a key variable.