A modelling evaluation of a system combining rainwater and greywater for potable water savings

This study aims to evaluate the potential for potable water savings by modelling the hypothetical installation of a system that combines rainwater and greywater in a house. The system consists of using rainwater to wash clothes and then reusing the effluent to flush toilets. The potential for potable water savings and the tank capacity for rainwater storage were estimated using the computer programme Netuno. A financial analysis was performed. For a rainwater tank capacity equal to 5000 litres, it was possible to obtain 51.6% potable water savings. The payback period was estimated as five years and three months. The system combining rainwater and greywater is a good alternative to save potable water because there was a significant reduction in potable water consumption and low payback period. The high potable savings and low payback period found in this work may contribute to the acceptability of these technologies and practices.