What is stormwater? What are its impacts?

What is stormwater? What are its impacts?


Boom nets are designed to trap and minimise stormwater gross pollutants from entering

Stormwater is rainwater plus anything the rain carries along with it. As rainwater runs across different surfaces, it can pick up various types of pollutants including:

  • sediment from exposed soil
  • oil and grease from driveways and roads
  • leaves and animal droppings that collect in gutters
  • chemicals from lawns and gardens.

In urban areas, rain that falls on house roofs, paved areas like driveways, roads and footpaths, or flows from saturated gardens and grass fields, is carried away through stormwater pipes and canals to the ocean, via creeks and rivers.

In the Sydney drinking water catchment, stormwater is carried, not to the ocean, but into local creeks and rivers that flow into major drinking water supply dams. This makes stormwater pollution from rural properties and towns in the catchment a major risk to the quality of our drinking water - a risk that everyone living in the catchment can help reduce.

Stormwater impacts

Stormwater running over rural land or from our catchment towns can pick up a range of pollutants:

  • dissolved chemicals from various sources including pesticides and herbicides
  • waste from livestock and pets
  • sewerage and effluent from falling onsite wastewater treatment systems
  • soil from ploughed paddocks, eroded land or construction sites.

Stormwater can also:

  • alter river flows
  • change flooding patterns
  • increase flow velocity, turbidity, erosion
  • affect the availability of water for irrigation.

Even plant seeds can cause problems, particularly if the stormwater also contains high levels of nutrients. Weeds can be spread downstream to neighbouring properties, bushland areas and national parks in the Sydney drinking water catchment.


Tuesday 17 May
2,573,926 ML
2,581,850 ML
9,342 ML
1,335 ML
50,768 ML
Tuesday 17 May