The Australian government manufacturers to allow 50 litres of hot water per person per day, as the 180L iStore can produce up to 1400 litres per day at 60 litres per hour we recommend the 180L for up to a family of 4 in a water conscious household with water saving showerheads. The 270L can produce up to 1900 litres per day at 80 litres per hour and suitable for large families.