Assessing the combined benefits of water recycling technologies by modelling the total urban water cycle

Urbanisation is one of the most significant sources responsible for additional pressures (both qualitative and quantitative) on the environment. Typical quantitative pressures are the temporal changes of the hydrosystem's water flow pattern (due to alterations of the terrain) and the water abstractions (due to the water demand increase). Sustainable, water-aware technologies, like Sustainable Urban Drainage Systems (SUDS) and rainwater harvesting schemes, can be implemented to reduce these pressures. These technologies introduce interactions between the components of the urban water cycle. Rainwater harvesting for example, apart from the potable water demand reduction, has significant influence on the generated runoff. Consequently, integrated modelling of the urban water cycle is necessary for the simulation of the modern water technologies and the identification of their combined benefits. In this study, two hypothetical developments, referred hereafter as development H and development L, that implement rainwater harvesting scheme and SUDS are simulated using the Urban Water Optioneering Tool (UWOT). The characteristics of the developments H and L correspond to high and low urbanisation density. The study is organised into three stages. The first stage includes the calibration of UWOT's rainfall-runoff module. The second stage includes the identification of the optimum configurations of the developments that minimise the environmental pressures. The final stage includes a sensitivity analysis aiming to investigate the influence of the characteristics of the water appliances and technologies on the generated runoff. This study indicated that: (a) the localised measures are more efficient than the centralised technologies for mitigating the runoff peak; (b) the cost to minimise the pressures of new developments on the environment increases significantly with the urbanisation density both because of the increased population and the increased sensitivity of the runoff's maximum on the development characteristics; (c) if localised rainwater harvesting is implemented then the efficiency of the water appliances influences considerably the generated runoff.