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Water outside a Liverpool home, a guide by Dotto

Mark 5 of 6 · a guide by Dotto

Stormwater and sewer are different

Stormwater is rain running off roofs, roads and paths, and it flows untreated to creeks, rivers and the ocean; wastewater is the used water from sinks, showers and toilets, piped away for treatment. Sydney Water’s policy keeps them apart both ways: no stormwater or roof water into the wastewater system, and no wastewater into a stormwater pipe.

Last checked 8 October 2026 · General information

Cross-section of a house and street. Rain from the roof runs down a downpipe into a stormwater pipe that leads to the street gutter and on to a creek. Water from the toilet and sink runs into a separate wastewater pipe that leads to Sydney Water’s wastewater main, for treatment. Downpipe Stormwater pipe Street gutter To a creek Toilet, sink Wastewater pipe Sydney Water main to treatment
Drawing, not to scale. Every property is different, and Sydney Water’s typical connection diagrams show the arrangements it uses.

Side by side

From Sydney Water’s stormwater, wastewater and responsibilities pages, read 8 October 2026.
ComparedStormwaterWastewater (sewage)
What it isRain that runs off roofs, roads, car parks, paths and driveways. The used water from sinks, showers and toilets. It is 99% water.
Where it goesOften from property drains to street gutters run by the council, then to channels, pipes and creeks. Through Sydney Water’s wastewater pipes, for treatment.
Is it treated?No. It flows into creeks, rivers and the ocean untreated. Yes. Treated wastewater is returned to the environment.
The owner’s partPrivate stormwater pipes, up to where they connect to Sydney Water’s network. Private wastewater pipes, up to where they connect to Sydney Water’s network.
Must not go inWastewater, and pollutants such as oil, grease, paint, soil and sediment, or detergent. Stormwater or roof water.

Why rain must stay out of the sewer

Wastewater pipes are designed to allow for some extra flow in wet weather, but during very heavy rain that may not be enough. Sydney Water names four ways the extra water gets in: cracks in pipes, joints that have failed, gaps around maintenance hole lids, and stormwater pipes connected straight to the system. Wastewater overflows often follow heavy rain.

Any place with wastewater pipes can have an overflow, Sydney Water says, from bushland, parks and waterways to the street and a home’s backyard. Wastewater contains bacteria, viruses and protozoa that can cause illnesses such as gastroenteritis through direct contact, and overflows can harm sensitive plants and animals. Stormwater overloading the network in heavy rain is also one of the causes of blockages that Sydney Water names.

A downpipe connected to the sewer is one of those direct connections: it sends roof water into the pipe that Sydney Water says overflows in very heavy rain.

What Sydney Water’s policy says

Sydney Water’s policy on customers’ responsibilities, issued in June 2020, sets out these rules for stormwater.

  • You must not discharge stormwater or roof water to the wastewater system.
  • Wastewater from a home or business may not go into a stormwater pipe or structure of any kind.
  • Stormwater that drains to its catchment must carry no pollutants: no oil, grease, paint, soil, sediment, detergent or wastewater.
  • Anything that could damage the quality of the stormwater in its system must be reported to Sydney Water straight away.

Where Sydney Water believes a property has an unauthorised connection, the policy says it will write asking the owner to fix it, and any damage to its assets, within 21 days. If the notice isn’t followed, it may restrict the water supply or disconnect the unauthorised connection. The owner is responsible for the private stormwater and wastewater pipes up to where they connect to Sydney Water’s networks.

What helps, from the yard

Sydney Water’s own list for keeping stormwater clean is short and practical.

  • Wash cars on the grass rather than hard surfaces, so detergent soaks into the soil instead of the drains.
  • Sweep leaves, dirt and rubbish away from gutters.
  • Give garden beds good borders, so soil doesn’t wash away.
  • Put grass clippings in the compost or on the garden, and pet droppings in the bin.
  • Take chemicals, pesticides, paints and oils to the council’s chemical clean-out service.

On the roof, NSW SES asks households to clear gutters, downpipes and drains regularly: blockages can trap water and make it overflow under the eaves into the roof cavity. For the ground around a new home, the NSW Government’s maintenance advice is to guide water drainage away from the house and make sure excess water drains from the property to the stormwater channels.

Stay out of the drains

Stormwater channels, drains, tunnels and maintenance holes can be dangerous; Sydney Water says they are safe to enter only for its authorised maintenance crews. The water in them can rise quickly and without warning, even when it isn’t raining; shallow flowing water can be strong enough to knock you over; and stormwater may carry dangerous chemicals and disease-causing bacteria. Sydney Water also asks people not to try to lift stormwater grates near footpaths and roads, even to fetch something dropped: they can be very heavy.

If you see anyone entering a stormwater drain, channel, tunnel or maintenance hole, Sydney Water asks you to report it on 13 20 90, 24/7. Its full page on the subject is stormwater systems.