Stormwater Treatment

Stormwater is any runoff from surfaces that ends up in the drains on our streets. This water flows into local creeks and can be a significant source of water pollution. How can everyone address this problem?

What is in Stormwater?

Runoff from roads, driveways, yards, roofs and footpaths makes up stormwater. This excess runoff carries leaves, litter, animal waste, car wash detergent, engine oil, fertiliser and sediment into local waterways. Large items like leaves and litter clog waterways. Sediments and oil clog the gills of animals living in the creeks. Fertilisers, animal waste and detergent can cause eutrophication, a toxic algal bloom.

Rubbish is carried into the River Torrens (South Australia) by stormwater flow (W van Aken 1995, CSIRO Science Image)

Stormwater Treatment

In a natural environment, water infiltrates into soil and is used by plants. In cities, hard surfaces such as roads and roofs, stop water being absorbed. Traditionally, this has been channelled into drains that lead to creeks and rivers.

The most basic way of treating stormwater is a physical barrier that collects rubbish. These may be grates or netting bags at the end of pipes and/or floating barriers by stormwater outfalls. Larger rubbish is removed, but these devices do not remove sediments or dissolved pollutants.

Floating barriers can collect buoyant rubbish like this barrier in Rockingham, WA (Calistemon 2019, Creative Commons)

Water Sensitive Urban Design (WSUD) improves water capture and treatment in urban areas so that local waterways receive smaller amounts of cleaner water rather than sudden rushes of highly polluted stormwater. Planners use permeable groundcovers, biofilters and rain gardens to increase infiltration and clean stormwater. A typical biofilter will incorporate a physical trap (grate or net), a sediment settling area and vegetation with drainage underneath. This three-stage process traps large solids and sediments, as well as removing dissolved pollutants. The treated stormwater can be re-used for watering public parks and ovals or be released into local waterways.

Local councils create biofilters to increase habitat and improve the quality of water flowing to local creeks and rivers (Image courtesy of Hornsby Shire Council at

How You Can Help Water Quality

Responsible actions by people can make a big difference to water quality in your area. You can help by:

  • Raking up leaves and bark in the gutter and placing these in the green waste bin or compost
  • Putting all rubbish in the bin and picking up any you see on the street
  • Cleaning up dog poo and putting this in pet waste compost or the general waste bin
  • Washing your car on the lawn or in a car wash
  • Not pouring paint, mop water, motor oil or anything else down the storm drain
  • Using pesticides and fertilisers sparingly – a native garden will require little of these

You can help the water quality in your local area by picking up rubbish and raking up leaves that can wash into stormwater drains