GRAF Australia
Blog · 2026-03-26
Underground rainwater tanks in Australia: how to choose Carat or Platin
Underground rainwater tanks store roof runoff below ground so you keep capacity without a bulky aboveground vessel. In Australia, GRAF Carat and Platin are the primary modular platforms sold and supported by GRAF Australia.
What you need before you size
Capture roof area (m2), postcode, and how the water will be used (irrigation, toilets, laundry or mixed non-potable). Council reuse rules and cover depth limits vary by city.
Use GRAF Australia design tools for a first-pass volume, then refine with your plumber or engineer. Quote through grafaustralia.com.au or 1300 131 971.
Carat vs Platin
Carat is the core modular underground family for most residential and commercial reuse installs. Platin suits lower or flatter profiles when excavation depth is constrained.
Pair the tank with inlet filtration and a pump or pressure system. Retail DIY listings are not the same as engineered GRAF packages with AU documentation and state sales support.
Not the same as an OSD tank
Rainwater tanks store water for reuse. OSD (on-site detention) tanks control stormwater discharge rates for council peak-flow limits. Confirm the planning condition before you specify.
Keep reading
Specify products
Need a GRAF Australia quote?
Call 1300 131 971 or send site details for sizing and supply.