Stormwater is water that runs off surfaces into drains. It’s not the same as rainwater, which falls on roofs and is cleaner.   

How stormwater gets contaminated 

As stormwater drains, it carries pollutants with it like litter, sediment and oil. These are a major cause of pollution in our rivers, creeks, lakes and bays. 

Most of the time it’s everyday activities that cause urban stormwater pollution, not major spills or industrial accidents. It’s important to prevent waste from our homes or businesses polluting stormwater drains.

Pollution of our waterways can be a result of many things, such as:

  • industrial runoff from workshops
  • people washing their vehicles in the street
  • general litter – like plastic bags, bottles and cigarette butts.
Stormwater can come from runoff from roof surfaces, roof/gutter downspouts, yards, gutters and streets. As stormwater drains into storm drain systems and outlets, it carries pollutants with it. Stormwater runoff ends up in local creeks, streams, lakes, rivers and the ocean.

Why stormwater pollution is a problem 

Population increases are impacting the quality and quantity of stormwater that reaches our waterways.  

Stormwater quality

The stormwater system takes rainwater from our streets and gutters into the closest waterway.

Unlike sewage, stormwater enters our waterways untreated. At the end of the pipe system there are options for treating stormwater. For example, with pollutant traps that remove large, non-biodegradable pollutants. But in most cases, it flows from our streets and gutters into our creeks, rivers and the ocean.  

Stormwater quantity

An increase of built-up areas causes more stormwater runoff to enter our drains and waterways. 

Stormwater drainage systems usually remove stormwater from urban areas as quickly as possible. This is to reduce the risk of flooding and prevent water stagnating. The increased volume entering waterways causes scouring (in-stream erosion) of waterways.

Read more about stormwater

How to use stormwater 

Types of stormwater pollution 

How to reduce stormwater pollution

Water guidance for business and industry

Reviewed 6 March 2020