The study introduces and describes a new “wastewater reclamation module” for the global hydrological model CWatM, evaluating the impact of the new module from a water quantity perspective by comparing observed and simulated river discharge for a case study location (Ayalon basin). This is an important area of research for (large-scale) hydrological models, with both aspects of water quantity and quality associated with wastewater have been largely overlooked and simplified in existing models. However, I find it somewhat difficult to fully follow the approach taken, and therefore I find that the manuscript would benefit greatly from a more comprehensive description of the three stages included in the workflow (i.e. pre-treatment; treatment; post-treatment), in addition to justifications for the assumptions made.

For example:

1. Line 115: “User-defined collection areas”. What exactly does this mean/ how is the service area of a wastewater treatment plant defined? How applicable is the methodology for applying in areas lacking detailed information on wastewater treatment plants (i.e. export share, designed HRT)? While not tackled directly in this paper, the authors state that this work “sets the plans of “developing global input data for wastewater treatment and reclamation”, but it seems to rely on plant-specific information that is not always readily available.
2. How is seasonality in produced wastewater (and therefore reclamation) accounted for in the model? Line 127 suggests daily influent versus daily treatment capacity is considered; but does produced wastewater from e.g. domestic and industrial water uses actually vary at that temporal resolution? Similarly, in some areas, treated wastewater reuse may only occur intermittently throughout the year. How would the model deal with this/ is there a scheme for allowing temporal variability in wastewater re-use?
3. Line 127: “excess wastewater is discharged into pre-specified discharge locations”. What exactly does this mean, and how are these specified? Are these specified discharge locations storage basins, or the surface water network itself (i.e. overflows)?
4. Line 140: How is the “surface area of treatment pools” estimated? Why is the estimated pool depth set to 6m? Then line 153 says the depth is set to 1m (does it differ for extensive and intensive systems; it is not clear)? Also, what is the rationale for assuming three treatment pools?
5. Line 173: “collected untreated wastewater is exported form the simulated region if the WWTP associated with the collection area does not exist”. Please elaborate, I do not understand what is meant here.
6. Line 178: How is it determined if a reservoir is accepting treated wastewater? What is the data source for reservoirs and their “associations” with wastewater treatment plants?

The case study and scenarios are interesting. However, the model is applied and validated against observed discharge in only a single basin; which is both water scarce and is already large reliant on treated wastewater re-use. I find it therefore difficult to assess the applicability of the proposed approach in other hydrological conditions and with different levels of data availability. Being a module of a global hydrological model, I can imagine the eventual intention is to scale up this to be applicable for modelling the globe. I understand the push towards a multi-resolution modelling framework, but I currently struggle to see how/if this wastewater module would be implemented at more coarse spatial resolutions and in more data poor regions.

In this manuscript, the authors introduce a new module that considers wastewater treatment and reclamation (WRTM) to the Community Water Model (CWatM). Additionally, the manuscript also provides model performance analysis of multiple scenarios with and without the new module as well as some additional wastewater balance analysis for a case study location (Ayalon basin). In general, the manuscript targets wastewater processing, which is an important aspect of research in large-scale hydrological modeling that is often overlooked. However, similar to RC1, I believe the manuscript still needs major revisions before it can be considered for publication.

Major comments:

1. Module variables: while there are brief explanations of each variable following equations, I find some of those explanations confusing. For example: line 109, “…a logical variable (e.g., Ddom).”, what do you mean by logical? Or line 110, “…share coefficient (Cs) representing sewer connection rates and leakages”, so does that mean if Cs is set at 100, the sewer system will have 100% connection with no leakage? Considering that this module is intended to be publicly used, it would be beneficial to both the manuscript and readers if the authors would provide a much more detailed description of the variables in Equ.1 on: (1) How can they be identified? (2) What are the ranges and units (if any) of each variable? And (3) What do specific values of each variable mean? Please consider providing additional sensitivity analysis on these parameters as well.
2. Module inputs: Table 1 has provided a summary of the model’s input; however, it is unclear to the reader what the specific temporal (hourly, daily, or monthly? Timeseries or fixed value?) and spatial (gridded or vector-based?) requirements of the local datasets which hindered the possibilities of replicating this manuscript results or future applications of new model users. Additionally, it is unclear which input is critical and which is optional making it challenging to consider applying the module in other data-limited regions.
3. Model calibration: results from Table 3 suggest that while there are significant improvements when the module is applied, the simulated dry season mean flow is still substantially higher than observed data. Additionally, results in Fig B1 suggest that simulated results overestimate ET substantially across the entire calibration period (line chart) while normalized differences are also high, where the majority of the basin in spring and many locations in summer have ~70 to >100%. Thus, please consider further improving the model performance and provide additional comparisons for the validation period as well.
4. Model validation: considering that this paper focuses on introducing a new module, I’m struggling to see a clear comparison of model performance before and after the module is applied. It is rather difficult to distinguish the difference between simulated and observed results in Figure 3, thus, please consider providing an additional figure showing the hydrographs in a shorter period (i.e., 1 year) and displaying results from all scenarios so that the comparison is more visually clear how the new module can improve model performance. Additionally, since wastewater inflow is also a factor in evaluating model performance, please consider adding additional statistical values in Figure 5 (i.e., NSE, KGE).
5. Study area: similar to RC1, I find it difficult to assess the applicability of the module with just validation of one basin/one gauging station. I’d suggest the authors consider adding additional analysis on other basins where there is either less or more data available.

Minor comments

1. Title, I believe the new module not only considers wastewater reclamation but also additional treatment time right, perhaps a different title that contains WRTM?
2. Line 91, “hyper-spatial resolution”, while 1km grid is relatively high-resolution compared to most global models, please consider editing this term across the manuscript since there are other small-scale models that can simulate wastewater process at much higher resolution.
3. Line 87, “MODFLOW6” and line 226, “Modflow”, are these two the same? If so, please be consistent across the manuscript.
4. Figure 2, currently, the legend is rather difficult to read with all the visualization mixed in. Please consider turning all areas outside of the study area to white color in the main map to make the figure more visible.
5. Figure 4, in-figure text size is too small, please consider increasing it.
6. Line 281-284, “… simulated evapotranspiration with a satellite derived product… the simulated monthly influent flows into the Ayalon WWTP with observed data…”, please reference these figures.
7. The “detrended values” shown in Figure 5 are not mentioned specifically anywhere in the main text, thus consider changing the text to have more linkage while adding more detailed information on the detrend technique. Additionally, there seems to be a clear increasing trend in the top panel of Figure 5, which might be eliminated if the authors consider running an additional spin-up period to stabilize the model.
8. All tables, table sizing, and alignments are inconsistent, please revise.

The manuscript titled “Wastewater matters: Incorporating wastewater reclamation into a process-based hydrological model (CWatM v1.08)” introduces a novel development by integrating a wastewater treatment and reclamation module into the CWatM model. This advancement is important as it incorporates human-related activities into large-scale hydrological modeling. The overall structure of the paper is sound and logically organized. However, several aspects of the methodology require further detail and clarification. Additionally, there are concerns regarding the model calibration and validation design, which could influence the results and their discussion. I recommend major revisions to address the methodology section and enhance the robustness of the model evaluation.

Detailed comments

Line 89: Please verify whether the acronym "WRTM" is correct or if it is a typographical error. The acronym for "Wastewater Treatment and Reclamation Module" should be "WTRM" rather than "WRTM". If it is a typo, please correct it throughout the manuscript.

Lines 122-124: Please clarify the criteria for defining a wastewater treatment plant (WWTP) with a hydraulic retention time (HRT) ranging from 24 hours to 2 days. Would it be intensive or extensive?

Lines 127-130: The description here is unclear. Line 127 states that if the influent exceeds the designed capacity, the excess wastewater is discharged to a pre-specified location. This implies that the inflow is managed below designed capacity by discharging excess wastewater. However, Line 128 mentions that treatment plants allow inflows to exceed the designed capacity, which appears contradictory. Please clarify whether "daily treatment capacity" and "designed capacity" refer to the same or different metrics.

Line 136-137: Please clarify what “an increase of 25% in the operational daily capacity” is compared to? E.g., compared to HRT = 1 day?

Lines 154-155: The term "total treatment time" is ambiguous. Is this time fixed for treating fully filled treatment pools, or does it vary based on the storage conditions? Please provide a more detailed explanation.

Line 180: How are WWTPs assigned to "associated reservoirs"? For instance, must the reservoir be downstream of the WWTP, or can users assign reservoirs to WWTPs freely? Please clarify.

Lines 266-267: Please clarify whether Scenario S2 was used for model calibration and if the calibrated parameters were applied across all scenarios. If so, this approach might not be appropriate, particularly in the context of the model performance evaluation discussed in Section 4.1 (e.g., Table 3). Scenarios S0 and S1 may underperform because they were not calibrated for these specific scenarios. Please explain why separate calibration for each scenario was not performed.

Figures

Figure 2: The reservoirs, canals, and other water features are difficult to distinguish due to the busy map. Consider increasing the transparency of the background map, removing it altogether, or using thicker lines to better highlight the water features.

Figure 4: The figure is confusing, as it is unclear which text corresponds to which circle. It would be helpful to use different colors for the text associated with the circles and the text indicating different flows to improve clarity. In addition, the texts in the circles are too small to see.