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What is the Difference Between Stormwater and Rainwater?

  What is the Difference Between Stormwater and Rainwater?If you are building a new home, there are a number of requirements that your local council might require you to meet. Depending on where you are located, one requirement might be effective stormwater planning and installation of a stormwater tank. This article is the first in a series of articles exploring the topic of stormwater and the importance of stormwater detention in property development. It explores the differences between rainwater and stormwater and how each source is used in Australia.

Difference of Rainwater vs Stormwater

Before getting into the functional differences between rainwater tanks and stormwater tanks, it is worth distinguishing between “rainwater” and “stormwater”. Obviously, stormwater comes from rain, so technically it can be considered rainwater. So then, you might wonder what’s the difference? Stormwater is the water that drains off a land area from rainfall. This includes rain that falls on rooftops, directed through gutters and downpipes onto land or into drains, as well as rain falling on ground surface areas such as roads, driveways, footpaths, gardens and lawns. Rainwater refers only to the rain that falls on the roof, which can be harvested into a storage tank prior to contact with the ground. Rainwater quality is much higher, since groundwater generally contains many more contaminants including soil, organic matter, fertilisers from gardens, oil residues from driveways and the like. In Australia, most properties are connected to a stormwater system. The stormwater system is kept separate from the sewer system. Unlike sewage, stormwater is generally not treated before being discharged back into waterways and the sea.

Use of Rainwater in Australia

Urban households typically pay for a connection to a reticulated, treated (mains) water supply, but costs can be significantly lowered by utilising harvested rainwater. There are many benefits that rainwater provides. Besides offering a fresh supply of water that you can drink provided your system is properly maintained, rainwater can be used to flush toilets, wash clothes, water gardens, wash cars, top up swimming pools and the like. Rainwater is also important for people who live in rural areas and farmers who need water for agricultural purposes. Some rural properties don’t have access to a reticulated water supply, so they depend upon surface water sources like rivers and waterways, dams and rainwater. When these other water sources dry up, then water needs to be transported at greater expense.

Use of Stormwater in Australia

Stormwater can be a valuable source of water to collect. Reusing stormwater can save potable water, reduce downstream environmental impacts and help prevent overflooding of the stormwater system. In fact, stormwater that is treated is commonly used to water public parks, gardens, sports fields and golf courses. Stormwater after being treated is safer, and as such becomes a “recycled water” supply. While stormwater is generally unsafe for human consumption, property owners can capture stormwater within their boundary and use untreated for low-risk purposes such as garden watering and toilet flushing. Treating stormwater can increase its uses, for example filling swimming pools, and depending upon the treatment, although often not recommended, even become a potable water supply.

Stormwater Detention Tanks

New houses often have onsite detention facilities constructed as part of their home drainage system such. Many include stormwater detention tanks which are intended to remain empty, except during periods of rainfall and for a short time thereafter. Unlike a normal rainwater tank, the distinguishing feature of a stormwater detention tank is that it is specially fitted with a valve to slowly release water over time. There are basically two options with a stormwater detention tank solution:
  1. use two water tanks, one to harvest rainwater and the other for stormwater detention, or
  2. use a specially made dual use water retention/detention system.
One might think simply storing water in a rainwater tank might be a good solution, however in heavy downpours rainwater tanks can quickly fill up. The emptying of stormwater in a detention tank means there is space available to detain water in future downpours. The slow release of water into drains from stormwater detention tanks helps to assist your local area with more manageable loads of water runoff. While water detention tanks are a solution, they are more like the last line of defence in dealing with stormwater runoff. You can effectively plan your property to be more sensitive to stormwater runoff by combining natural solutions with effective design. If you are looking for stormwater retention or detention tanks for your home, talk to our team for expert advice on your property needs.