What is stormwater?

When it rains in urban areas, water runs off hard surfaces like roofs, roads, car parks, paths and driveways into stormwater drains. Stormwater eventually flows into creeks, rivers and the ocean.

Our stormwater system

Being safe around stormwater

Stormwater drains can be very dangerous places. This is why stormwater drains are often fenced and have warning signs telling people to stay out.

It's important that you don't go into drains – even during fine weather. It's also a good idea to keep pets away from drains.

Stormwater drains can be open channels or underground tunnels. They are dangerous because:

  • water in drains can rise quickly and unexpectedly, even when it's not raining in the local area
  • huge amounts of water can suddenly wash into the drain when it rains
  • you may not be able to get out of a stormwater drain if you're swept away by water – you could even drown
  • even shallow water can be very powerful and could knock you over
  • drains can contain pollution like broken glass, dangerous chemicals and disease-causing bacteria.

Don’t try to lift stormwater grates near footpaths and roads, even if something has accidentally dropped down. These grates can be very heavy.

If you're in a flooded area, stay away from roads, footpaths and areas where you can’t clearly see where you're walking.

Stormwater drains are dangerous.

Keeping stormwater clean

What's in stormwater?

Water is a solvent, which means it dissolves things. Wherever it travels, water carries chemicals, minerals and nutrients with it. 

Stormwater carries all the things that collect on hard surfaces, like roads, footpaths, driveways and roofs. Some examples of things in stormwater are:

  • litter, like plastic bottles, food packaging and cigarette butts that people leave on the street
  • oil and grease from cars
  • dirt, leaves and twigs
  • animal and bird droppings
  • chemicals, including nutrients, from washing the car on the driveway or road.

How is stormwater quality managed?

Unlike wastewater, stormwater isn't treated before flowing into creeks, rivers and oceans. We (and many councils) manage stormwater using stormwater quality improvement devices (SQIDs).

SQIDs are designed to catch solids so they can be removed from the water, such as:

  • trash racks
  • sediment traps
  • litter booms
  • constructed wetlands.

In the past 20 years, we've installed 70 SQIDs. These devices have helped remove over 35,000 cubic metres of litter and organic waste as well as 39,000 tonnes of sediment from stormwater before it reaches Sydney’s waterways.

Learn more about what we're doing to manage stormwater.

Stormwater Quality Improvement Devices (SQIDs) collect rubbish from waterways.

What can you do to help?

You can help us keep our waterways clean by:

  • putting rubbish in the bin
  • washing cars on the grass instead of hard surfaces so detergents wash into the soil rather than stormwater drains
  • sweeping leaves, dirt and rubbish away from gutters
  • making sure your gardens have good borders so soil doesn’t wash away
  • putting grass clippings in the compost bin or on the garden
  • picking up your pet’s droppings and putting them in a bin
  • disposing of chemicals, pesticides, paints and oils using your local council's chemical clean out services. 

Stormwater audits

Identify pollutants in your stormwater drains and help keep waterways clean.

Using water-sensitive urban design

What is water-sensitive urban design?

It's important to consider the water cycle as part of our built environment. When the water cycle is included in planning, designing and constructing our built environment it's called water-sensitive urban design (WSUD).

Our built environment often includes hard surfaces, like roofs and roads, that interrupt the natural water cycle processes of run-offinfiltration and percolation. WSUD concentrates on making sure these processes can still happen.

When using WSUD, we have to take lots of things into consideration. Learn more about water-sensitive urban design (553KB).

A lot of design work goes into managing stormwater.

Safety – Can we use design to reduce dangers like drowning?

Maintenance – Who will maintain the area after it's built? How?

Water quality and quantity – What quality and how much water is flowing in? What quality is the receiving environment?

Available space – How much land does the design use? What habitat or land features will be impacted?

Climate – What are the rain patterns? Will the design need to cope with high volume, infrequent rain events or low levels of rain over a long period of time?

Landscape – What is the topography and slope of the land? What type of soil is in the area? Different soils have different percolation rates.

Community – How will the area be used by community?

What are the features of water-sensitive urban design?

There are many features that can be used individually or together to make a design more water sensitive. 

Features can change how the water flows through the environment and improve water quality.

Using the table below, decide which feature you would use for these scenarios:

  • Stormwater that has no fine sediments but lots of plastic drink bottles. 
  • Stormwater that runs off a large car park and carries lots of fine sediments.



Good for

Vegetated swales

Water flows through a wide, shallow channel made out of gravel and soil. Plants growing in the channel slow the water down, encourage sediments to settle and capture litter and organic matter.

Removing litter, organic matter and fine sediments.

Sediment basins

Water flows into a basin (pond) that encourages the water to slow down and sediments to settle.

Removing litter, organic matter and fine sediments.

Constructed wetlands

Water flows into a large man-made wetland that has design features that encourage settling, biological treatment and fine filtration. Lots of plants are used to enhance the treatment and provide habitat for wildlife and fish.

Removing fine sediments, nutrients and heavy metals.

Gross pollutant trap

A physical barrier that traps litter and large organic matter (leaves and twigs) as the water flows through.Gross pollutant traps need to be cleaned and the rubbish taken away. 

Removing litter and organic matter.

Porous pavements

Porous pavements allow water to infiltrate through a surface, rather than run off it. They can be used for footpaths, carparks and areas next to roads.

Removing fine sediments.

Sediment basins are designed to slow water down so sediments can settle.

Constructed wetlands are good at removing nutrients, sediments and heavy metals.

Water-sensitive urban design – case studies

Creating a green, cool, resilient city requires a shift towards water-sensitive planning and design.

By improving the flow of water through the natural and built environment and using and reusing water more wisely, we can achieve these outcomes:

  • cooler temperatures and reduced energy demands
  • improved waterway health and habitat
  • increased canopy cover and retain vegetation
  • increased open spaces
  • less money spent on infrastructure to capture and treat run-off
  • reduced impact of flooding.

Building our green, cool, resilient city with WSUD.

Here are some examples of some projects we have been working on.

Checking stormwater connections

Wastewater and stormwater are managed using 2 separate pipes and plumbing systems:

  • Wastewater is used water that goes down toilets, sinks and drains and into the sewerage system. 
  • Stormwater is rainwater that runs off hard surfaces like roofs and roads and is carried away by stormwater drains flowing into local waterways.

How can stormwater enter our wastewater system?

When a stormwater pipe is connected incorrectly or rain can enter the wastewater system it can cause overflows, impacting the community and the environment. 

The condition of stormwater connections can be checked using a couple of methods:

  • smoke testing – a small amount of environmentally safe, non-hazardous smoke pumped into wastewater pipes to identify possible leaks and incorrect connections. 
  • visual inspection – a visual check of external downpipe connections and outdoor drains

Did you know as a property owner, you have a role in maintaining the wastewater pipes and stormwater downpipes on your property.

Downpipes are connected to roof gutters.

Harvesting stormwater for recycling

Collecting and treating stormwater so it can be recycled is called stormwater harvesting.

Stormwater harvesting can help reduce demand on drinking water supplies by providing another water source for things like:

  • watering sports fields and gardens
  • flushing toilets
  • washing machines (in some cases).

These activities don't require water to be treated to a drinking water standard.

Finding practical and cost-effective stormwater harvesting options is a challenge. Some of the problems are:

  • finding suitable space to build large storage and treatment facilities
  • treating the stormwater so it's good quality
  • finding efficient ways to reuse the water, including transporting the treated stormwater to where it's needed
  • making sure stormwater harvesting doesn't damage waterways by reducing natural flows.

Flood mitigation

Sydney has a variable climate. We can’t always predict when it will be dry or it will rain.

Heavy rain can cause urban waterways to rise quickly. It may take only minutes for fast-moving floodwater to fill a waterway.

We work closely with local councils and other agencies to improve the health of our stormwater system and protect people and properties from flooding.

Our current projects will help protect people and their property from flooding during storms and heavy rain.

To be active in what is happening in your local community, we have Sydney Water Talk. Customers get to share their opinions about projects, so you can help us shape and create liveable communities.

Learn more about how to minimise your flood risk with SES NSW education programs.

Stormwater channels can contribute to liveable communities.

Self-guided excursions

We'll help teachers set up their own local waterway excursion.


Rainwater that runs over the Earth’s surface and into waterways rather than being absorbed into the soil.


Water that soaks into the ground during and after rain.


Percolation is when water seeps deeper into tiny spaces in the soil and rock.