Environmental issues


Stormwater pollution

Types of stormwater pollution

There are four main types of stormwater pollution:

  • litter, such as cigarette butts, cans, paper or plastic bags
  • chemical pollution, such as detergents, oil or fertilisers
  • 'natural' pollution, such as leaves, garden clippings or animal droppings
  • sediment pollution, such as soil erosion and runoff from building sites and unsealed roads.

This ends up discharging into waterways as sediment, sludge and solids. These can be caught in stormwater treatment measures, but the most effective way to reduce this problem is to prevent pollution entering the stormwater system in the first place. The traps don't catch all the silt or litter, and they don't stop chemicals.

Who's responsible?

Everyone has a part to play. Reducing the pollution depends on every person preventing harmful natural or chemical substances entering the drains.

Council is responsible for controlling and maintaining stormwater systems. However, it is everyone's responsibility to reduce the amount of rubbish and pollution that is carried into the drains. Local councils and rate-payers have to foot the bill for cleaning out pollution traps, and it's much more cost-effective to stop the problem at the top of the pipe  than further downstream.

Factors affecting stormwater pollution

The quantity and severity of stormwater pollution are affected by:

  • when it last rained and the intensity of the rain
  • building density and other land uses in the catchment area
  • level of vegetation cover
  • the cleanliness of the streets
  • local practices, such as street sweeping, pet control, garden watering, or use of chemicals.

Pollution at home and in your street

Typical activities that can cause stormwater pollution are:

  • car washing on the street: using detergent and allowing it to run down the street drain.
  • fixing your car on the street: letting oil or other substances flow into the street drain
  • disposing of garden waste: letting leaves or garden clippings accumulate in gutters or driveways where they can end up in the street drain.
  • dropping litter: dropping litter where it will be swept into the street drains next time it rains.
  • cleaning paint brushes: letting the contaminated water flow into the street drain.  
  • hosing the footpath: letting the water carry dirt, soil or other waste into the street drains
  • not picking up dog droppings: left dog droppings will be carried into the stormwater system next time it rains. (Imagine the cumulative effect of all the dogs in your neighbourhood.)

Pollution at work

Typical activities at work that can cause stormwater pollution are:

  • restaurants: not cleaning out the grease trap regularly
  • motor vehicle repairers or printers: letting oil, chemicals or other waste flow into the street drain
  • builders: not shielding street drains from spilt chemicals or excess soil, sand, gravel or other building waste
  • all work places: letting cigarette butts or litter fall into gutters or on driveways; letting chemicals, detergents or other harmful fluids run into street drains.

Effects of stormwater pollution

Effects on plants and animals

Stormwater pollution can kill plants and animals that live in the water. For example:

  • sediment in the water reduces light penetration and affects photosynthesis, the process that allows plants to use light as their source of energy
  • when green waste decays in water it uses up oxygen, taking vital oxygen away from plants, fish and other aquatic animals
  • soil makes waterways cloudy and can suffocate fish by clogging their gills
  • litter clogs waterways and causes toxicity as it breaks down. It affects the health of birds, fish and other animals and plants that live in the waterways.

Effects on humans

Stormwater eventually feeds into our waterways. Healthy waterways mean a healthy future for the environment and the economy — and for us. For example:

  • bacteria and viruses in stormwater can pose a health risk to humans. It can be dangerous to swim immediately after rain
  • ugly pollution destroys the visual amenity of our waterways

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Page last updated: 04 October 2013