Review of 'Assessing SDG indicator 6.4.2 “level of water stress” at major basins level'

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.