Enter roof area, annual rainfall and household size to calculate collection potential and recommend the right tank size.
Auckland ~1200 mm, Wellington ~1250 mm, Christchurch ~650 mm
For a family of 4 using rainwater for toilets only (25 L/person/day = 100 L/day), a 5,000–10,000 L tank provides 50–100 days of storage. For full household use (600 L/day), a 22,500–30,000 L tank is typically needed. This calculator recommends the right size for your situation.
Multiply roof area (m²) by annual rainfall (mm) to get litres per year, then apply an 85% collection efficiency for losses. A 150 m² roof in Auckland (1200 mm rain) collects approximately 153,000 L per year.
Yes, but it requires treatment per NZS 4509:2008 (Onsite Domestic Rainwater Supply). This typically includes first-flush diverters, tank covers, filtration, and UV or chlorination treatment. Check with your regional council for local requirements.