The Australian and New Zealand standard, AS/NZS 3500.3:2015, Plumbing and Drainage, Part 3: Stormwater drainage, provides design, installation and other information for roof and property drainage systems.

The design method for surface drainage systems is a simplified rational method procedure that can be implemented on a spreadsheet. The intensity used is for a 5 minute duration storm from the 1987 Australian Rainfall and Runoff rainfalls. ARIs are selected according to consequences of failure from a table in the standard.

Different procedures are given for Australia and New Zealand, reflecting past practices and local standards. Only the Australian method is provided in DRAINS.