Rainwater Harvesting (RWH) systems are recognized as a widely accepted
solution to save potable water in buildings. In addition, RWH systems may play an
important role in mitigating the impact of increasing imperviousness in urban areas by
contributing to increase both at-source retention and detention of storm water runoff.
The chapter provides an overview of methodologies for designing RWH systems, with
specific focus on numerical models based on the long-term water balance simulation of
the tank. An overview of metrics to evaluate RWH system performance is presented,
with regard to the estimation of both water saving potential and storm water control
benefits. The accuracy of the modelling results with reference to the length of the
available rainfall series and to the selected resolution time step of the used model is
discussed. Results of an application to six cities in southern Europe are also discussed
in order to highlight the impact of different precipitation regimes as well as the
influence of rainwater demands on the system design and performance. Finally, the
German, British and Italian standards on RWH are analysed and compared to identify
differences and common design approaches.
Keywords: Behavioural model, Detention time, European standards, Long-term
simulation, Operational parameters, Precipitation, Rainwater harvesting,
Rainwater demand, Runoff control, System performance, Tank sizing, Water
saving, yield.
