Difference between stormwater and sewage

Difference between stormwater and sewage

so what’s the difference between stormwater and sewage? In Australia, the stormwater system is separate from the sewer system. Unlike Sewage, stormwater is generally not treated before being discharged to waterways and the sea. Due to the lack of treatment infrastructure for stormwater, it is important to try and minimise the environmental impact of the stormwater from your property.


In urban areas, stormwater runoff is generated from the rain that falls from roofs and drains down to the land, driveways, roads, and other impervious surfaces. This runoff picks up and carries pollutants such as soil, organic matter, litter, chemicals (oils and fertilisers) downstream and into our waterways.

This is different from rainwater which is the water that initially falls onto the roof and travels down gutters, downpipes, and into water tanks or onto the land as stormwater. Rainwater is usually cleaner and can be used for reuse purposes which can save potable water and reduces downstream environmental impacts.


Sewer drainage (also known as Sewerage) is the collection of underground piping that carries all the sewage (waste from your home) to a treatment plant to be treated before being discharged into our waterways. This removes most of the pollutants and chemicals, basically separating water from sludge and allowing the cleaner water to continue. this is effective as sewage is technically 99% water.

Better manage your stormwater and reduce your environmental impact

Simple steps that all homeowners can take to better manage their stormwater and reduce their environmental impact include:

  • Avoid cut and fill on your block when preparing the building foundations. Attempt to maintain the existing topography and drainage pattern.
  • Retain vegetation, particularly deep-rooted trees. They lower the water table, bind the soil, filter nutrients, decrease runoff velocities, capture sediment and reduce the potential for dryland salinity.
  • Minimise the area of impervious surfaces such as paved areas, roofs and concrete driveways.
  • Grade impervious surfaces, such as driveways, during construction to drain to vegetated areas.

Water Sensitive Urban Design (WSUD) slows the runoff rate of stormwater and improves filtration and infiltration.

  • Avoid solvent-based paint. After using paints, clean brushes and equipment on a lawn area to trap contaminants before they reach waterways. Plant-based paints are more environmentally safe.
  • Go to carwashes that recycle the water or wash your own car on the lawn or area that drains down to the lawn. Nutrients such as phosphates and nitrates in the detergent fertilise the lawn instead of degrading the waterways. Note that many native plans do not tolerate detergents.
  • Do no build over floodplains which have a risk of flooding. Councils can advise on the 1 in 100 year flood level.

read more in Australia’s guide to environmentally sustainable homes

Stormwater Sydney provides Inspection, Cleaning, Maintenance, Repairs, Construction, and Advisory on stormwater systems across Sydney, ensuring compliance with Sydney standards and Council regulations.

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