I enjoyed reading this manuscript. I also applaud the authors for such a nice contribution to the modeling community. Given that GMD is highly interdisciplinary and has a broad audience, I encourage the authors to better define some terminologies upfront. A few specific, minor comments are listed below.

1. Line 26-28. "water cycle" --> "terrestrial water cycle" since the components listed here do not include atmospheric or ocean components. It seems different people have different definitions or understandings about the "components" in a water cycle. To help the readers better understand, a conceptual diagram might be useful here to illustrate the various components (particularly those represented in the model) and their physical and anthropogenic linkages. Lastly, by "hydrological catchments" do the authors mean the surface areas where rain falls and runoff is generated and routed into rivers? If so, I'd suggest placing it at the very beginning of this list, since the terrestrial water cycles (at the catchment, regional, or global scales) begin with rainfall and runoff processes. 

2.  Line 28. What is the difference between "hydrological catchments" and "river catchments"? If they are the same, please just use "catchments" after the definition upfront. 

3. Line 74, "abstracts". Please use another word if possible to avoid confusion. For example, "abstraction" could mean "rainfall infiltration and/o retention" to some hydrologists.

4 . Line 457-460. It would be better to move this example upfront in the introduction, perhaps along with another couple of classic ones. This way, the readers will have a better sense of what are "boundary conditions" and then the authors intend to achieve. I did not get this puzzle resolved until reading to this point.

The authors present an open-source Python tool to make integrated model of the water cycle, including water quantity and quality. They start with a review of the state of the art, then present the conceptual structure of the model, very briefly introduce a demonstration and then focus on discussing the need for the tool. Finally they present some conclusions.

The work that the authors present is interesting and, in my opinion, within the scope of GMD. Their tool being a library, may serve to others researchers to adapt it to their needs, either using the already developed classes, either by modifying the code. I think the paper may deserved to be published in GMD, however I have a major concern about the paper structure.

Section 2 presents a conceptualization of the model, which is not evident to follow. Such a conceptualization is important, because it allows to extend the model in an easy way and to represent similar elements with a minimal amount of code. However, conceptualizations are difficult to grasp, so I would suggest that the authors combine section 3 (which currently is not very illustrative, probably because the link provided is not working for me -I get a 404 error-) with section 2 in such a way that they first explain a canonical case in water management, that anyone could understand, and from there, they present the conceptualization.

In this way, the reader would be able to put "some meat" in the concepts presented, making it easier for the reader to apply the WSIMOD software to their own problems. Without such a change, the presentation may not be clear enough to ensure an understanding.

Moreover, after having checked the paper where the source code was published, I am also missing some more technical details. They may be better suited to supplementary material, but I believe that an explanation of the technical details and equations behind the model elements would be interesting. Not only to have all that information in a citable location, but also to have it all concentrated in one place, so that when problems arise, the users of the library may try to troubleshoot problems with the equations looking at just one section of the paper. (This information may be somewhere in the documentation, but I have not been able to find it).

* Minor comments

+ Line 19/20: Improve use of verbs.

+ Line 201: "our" seems to be out of place.

+ Line 354: adjudged may not be the term the authors intended to use