Keep up to date with our innovations

Stormwater Retention vs Stormwater Detention

Commercial development projects need to take care of stormwater with a detention tank, a retention system or both. Discover the difference between the two.

Developing a commercial property in Australia comes with a number of requirements. One of these is to find and implement a suitable solution for managing stormwater run-off. 

Basically speaking, if your development is set to replace the earth with concrete, you need somewhere for heavy rain to go, otherwise, the local area is at risk of being flooded. 

There are different options for the stormwater management system you choose, depending on the way you can use excess water. One is stormwater retention, the other is stormwater detention.

Even though there is very little difference between the words retention and detention, when it comes to stormwater management, the two are definitely not the same.

Concrete prefabricated tanks installed underground for rainwater harvesting.
Round anti-floation tanks installed for rainwater harvesting.

Stormwater retention systems/water harvesting

When you install a stormwater retention system, it is with the intention of collecting and storing water for reuse. The same way you would with a house’s grey water, the water goes into a tank and is then reused for things like flushing toilets or washing vehicles. The water isn’t fit for consumption, but if you can find a way to use it around the property, choosing a stormwater retention system makes sense. 

This water harvesting solution is environmentally friendly and can help to reduce the operating costs of operating a commercial building. At Australian Tanks, we have installed stormwater retention solutions on sites including: 

  • Defence sites at Enoggera, Oakey, Canungra and Greenbank, Richmond NSW, Eclipse Hill WA.
  • Fuel stations and commercial developments
  • McDonald’s stores throughout Queensland and New South Wales
concrete on site detention tank installation
Modular OSD tanks installation for on site detention.

Stormwater Detention Tanks – OSD

Stormwater detention refers to the process of temporarily holding stormwater and slowly releasing it back into the public stormwater system at a controlled rate. This is to ensure that floodwater doesn’t overwhelm the environment. 

The acronym you will come across is OSD, which either stands for Onsite Stormwater Detention or On-Site Detention. 

The rules for the types of buildings that require stormwater detention depend on the state where you are based. For more specific regulations consult your local council, however, the general rule of thumb for properties requiring OSD across Queensland, New South Wales, Victoria and the rest of Australia includes (as shared by Sydney Water):

  • all commercial, industrial and special use (for example, community, education, recreational) buildings or structures.
  • townhouses, villas, home units or other strata subdivisions. These may use a single OSD system for the total site area if it’s located on common property and the body corporate is responsible for maintenance.
  • dual occupancy lots. Each lot within the dual occupancy must have its own OSD system. Each individual lot owner is responsible for maintenance.
  • sealed sporting facilities (for example tennis, basketball courts).


Which type of stormwater tank is right for your development? 

Stormwater retention systems and stormwater detention tanks can both be installed as an underground solution. You cannot put a multi-storey building on top of an underground water tank, so they usually sit adjacent to a building or under the car park.  

The stormwater management system you choose will depend on the needs and purpose of your development. If you are able to reuse stormwater, it will make sense to choose a retention system. In other cases, an OSD may be more appropriate. At times, the solution may involve a mix of stormwater retention systems and stormwater detention tanks.

Parthenon OSD tank installation with crane and trucks
Parthenon OSD tank installation for on site detention.

The size of the stormwater detention tank or stormwater retention system you require will also depend on the size of your project. Tanks start from 100,000 – 200,000 litres and there are models that can hold up to 800,000 or even 1 – 2 million litres of water. 

There are more than basic tanks involved with stormwater management. Things like filtration also come into play, which is why your project needs tanks that are compatible with all the different filtration systems on the market, or to find a ‘turnkey’ solution. Underground tanks also need to connect with existing plumbing infrastructure at the right level. It makes sense to look for a tank supplier that keeps both of the above in mind. 

Choosing the right stormwater management system will depend on the needs of your project, as well as local regulations. Visit our Engineers Hub to view the specifications and capacity of our stormwater tanks, or contact Australian Tanks to find out more.

Read our Latest Articles
Connect with us
Sign up to

We pride ourselves on our service

Australian Tanks could never have grown to where it is now without our valued customers. Our attention to detail is why our customers keep returning to solve their water storage solutions. We want nothing more than for our customers to enjoy the longevity and efficiency of our commercial water tank solutions, which is why we work as closely with our customers as possible to find the best solution. Check out some of the things our favourite customers have said about us!

Nick Rees
Context Engineering
Australian Tanks products are easy to specify on a drawing – they’re easy to size, and are workable within most site constraints.
Bruce Rob
Group General Manager
HWB Group
Thanks to the team at Australian Tanks for getting this key piece of site infrastructure in place in such a short space of time despite rain and allowing the site access back in use quickly. Well done to our BUILDUS team for getting on with the job.
Adam Williams
Managing Director
Platinum Hydraulic Design
The professional manner in which Australian Tanks approached this project resulted with the successful installation of several large capacity grease interceptor traps that are fully compliant with the City of Gold Coast Trade Waste Department requirements. Congratulations to Les Green and Team for the professionalism, and a quality product.
Aaron Glowka
Project Manager
The service from the team is outstanding, they’re always available to help. They’ll do whatever they can including come out and work you to get it right. The different volume tanks are brilliant! Standard sizing that you can adjust the volume makes it uniform when working across different jobs. Consistency in area for planning also helps to save time and money in the long run!

All our product specs any time.

Are you planning for an upcoming project? Our Engineer’s Hub can help you find the product you need, quickly and easily.

Every detail is here for you when you need it, at your own leisure, to help you discover what is the right fit for your project.

Gain access to all the required plans to determine which product meets your needs and be able to specify the solution into your design with downloadable CAD drawings.

Complete access to all our documents