Rainwater harvesting systems

Underground (Carat, Platin, Lilo, Sapphire, Herkules buried) keeps water cool and dark, hides the tank from the garden, and suits house reuse for toilets and laundry. Above-ground (Slimline, Round, Herkules above-ground) is faster to install when dig is blocked by rock, trees or services. In hot Australian climates, keep above-ground tanks opaque and out of harsh sun where possible.

Choose Platin when excavation depth is limited (rock, high water table, shallow services) or you want less spoil and a shorter dig. Carat is the usual choice for deeper installs and larger house packages. Both are groundwater-stable options in the GRAF Australia range when specified correctly.

At minimum: a filter upstream of storage, a tank, and a way to extract water (garden pump or automatic house package). Garden-only setups can be simple. For toilets and laundry you typically specify a Carat or Platin underground tank with an Optimax / Compact filter package, a pump, and a domestic waterworks / controller that can switch to mains when the tank is empty. Always use a separate non-potable network, never cross-connected to drinking water.

Underground tanks such as Carat and Platin keep water cool and dark, which limits algae growth and helps quality stay consistent. Above-ground tanks (Slimline, Round, Herkules) should be opaque and sited out of harsh sun where possible. Always filter before the tank so leaf litter and coarse debris never enter storage.

Volume depends on three things: local rainfall (BOM / postcode), effective roof catchment area, and demand (irrigation, toilets, laundry). Australian projects often size for dry spells and council WSUD targets, not only average annual rain. Share roof m², postcode and reuse intent and we will recommend Carat, Platin, Sapphire or above-ground options from the catalogue.

Yes. Rainwater is soft (low mineral content), which can reduce detergent use and scale compared with hard mains water. Route it only through a dedicated non-potable reticulation with clear labelling. Confirm plumbing, backflow prevention and any water-authority notification requirements for your state and council before connecting toilets or washing machines.

With a filter upstream and a working overflow, underground tanks typically need desludging only every 10 to 15 years. A thin sediment layer on the floor is normal and helps quality. Do not over-clean. Floating matter is flushed via the overflow siphon when the tank overflows. Self-cleaning Optimax-style filters usually need a quick check once or twice a year depending on leaf load.

Requirements vary by state and local council. Plumbing work should follow the Plumbing Code of Australia / AS/NZS practice and licensed installers. Using rainwater inside the house (toilets, laundry) may need notification or approval from your water utility for the dual supply. Always check local building, plumbing and stormwater rules before install. GRAF Australia can help with product documentation for submissions.

Underground tanks need a controlled overflow to stormwater, sewer (where permitted) or on-site infiltration / detention. Keep the overflow above backwater level and fit a flap valve where required. Above-ground tanks should use a downpipe filter that diverts excess to the stormwater system once the tank is full, so the downpipe never surcharges into the building.

Most Australian sites do not need European frost-depth bury rules, but alpine and inland cold pockets still need buried suction lines and fittings protected from freeze. Above-ground tanks in frost-prone areas should be drained or isolated in winter if they can freeze solid. Confirm local practice with your installer.

Many GRAF underground tanks (Carat, Platin and larger formats) can take pedestrian or vehicle loading when fitted with the correct cast / concrete cover and installation detail. Match the lid and traffic class to the driveway or car park. We will nominate the right cover with the tank package.

Some councils and states offer rainwater-tank rebates or stormwater credits for retention and reuse. Schemes change often, so check your local council, water retailer and any BASIX / planning conditions. We can supply product specs to support rebate or DA documentation.

Four stages in a typical underground package: (1) Optimax / Compact filter cleans inflow and rinses debris away; (2) calmed inlet lets fines settle without stirring the tank; (3) overflow siphon removes floating matter (e.g. pollen) when the tank spills; (4) floating intake draws the cleanest water from about 10 cm below the surface for the pump. That is the same multi-stage approach GRAF documents internationally, specified here with AU catalogue products.