A Rainwater-First Roof and Storage System for a Water-Short Household: Integrated Sizing of Roof, First-Flush Diverter and Tank Against a 450 mm Rainfall Regime

Integrated sizing of roof, first-flush diverter and storage tank for a water-short household, computed together against a stated 450 mm per year rainfall regime at 100 litres per day demand for five people. SIMULATED, NOT MEASURED; nothing was built or hardware-tested. A 120.0 m2 roof plan, a 120.0 litre first-flush diverter removing a computed 94.3% of modelled wash-off load, and a 20,000 litre tank supply the full demand on 352.23 days per year on average (96.50% full-day reliability) in a 30-year seeded daily simulation. A 10,000 litre tank reaches only 88.93%. In drought at 60% rainfall, reliability falls to 57.12%.