This paper proposes a new hybrid input-output model designed to analyze both the generation and treatment of wastewater. This model, named wastewater treatment input-output model (WWIO), can be regarded as an extension of the waste input-output model (WIO). As an application, I compiled the Tokyo Metropolitan WWIO table for 2000, which comprises 482 economic sectors, 11 wastewater treatment sectors, 12 types of wastewater-related waste and 6 types of environmental load. The model was applied to different scenarios to compare alternative wastewater treatment systems. The results indicate that replacing the simple treatment with the high-class treatment improves the quality of treated water while increasing CO2-equivalent emissions. Meanwhile, when the dewatered sludge is incinerated instead of landfilling, both CO2-equivalent emissions and landfill volume decrease.