Wastewater matters: Incorporating wastewater reclamation into a process-based hydrological model (CWatM v1.08)

Abstract. Wastewater treatment and reuse are increasingly perceived as essential to improve water use efficiency and increase water availability and reliability. Furthermore, wastewater has a significant impact on hydrological signals in urban watersheds. Hydrological modeling has developed over the last few decades to account for the human-water interface. Yet, despite the importance of wastewater treatment and reclamation, it is not yet comprehensively included in large-scale and multi-resolution hydrological models. This paper presents the newly developed wastewater treatment and reclamation module as part of the hydrological Community Water Model (CWatM) and demonstrates its capabilities and advantages in an urban and watershed with intermittent flows. Incorporating wastewater into the model increases model performance by better-representing discharge during the dry period. It allows for representing wastewater reuse in different sectors and takes on a modular approach, allowing for higher control over the wastewater treatment and reclamation process when spatial resolution and data availability allow it. As the current development focuses on water quantity, the water quality dimension of wastewater treatment remains a limitation, which sets the plans of incorporating water quality into the model and developing global input data for wastewater treatment and reclamation.