Rain under a deck belongs in the stormwater system and never the sewer: Sydney Water forbids letting any rain or stormwater into your property’s wastewater pipes. From a property, stormwater often flows to street gutters operated by local councils, and from there into larger channels, pipes and creeks.
Following one drop
Onto hard ground
Rain that can’t sink into the soil, because it lands on a roof, a road or a path, becomes stormwater, as Sydney Water puts it.
Into the property’s drains
According to the City of Sydney, owners look after the water pipes serving their property, shared ones included, no matter where on the land they run.
Out to the street gutter
From a property’s own drains, stormwater commonly heads for the kerbside gutter, which the local council runs. Connecting a private stormwater drain to a council’s underground system is a separate approval: the City of Sydney, for example, runs an application for it.
Into channels and creeks
From the gutter it can pass into bigger channels, pipes and creeks. Sydney Water’s own stormwater network serves about 645,000 properties in Greater Sydney; for a block inside one of its catchments, run-off ends up in a Sydney Water pipe, channel, creek or wetland.
Why the sewer is off limits
Sewers have some room for wet weather, but Sydney Water says very heavy rain can be too much for them. Rainwater finds its way in through broken pipes and poor joints, past the lids of maintenance holes, and through stormwater pipes plumbed straight into the sewer. Heavy rain is one of the usual causes of sewage overflows, Sydney Water says.
Under a deck, the sewer is close by in another way too. Sydney Water’s guidelines for light structures over small sewers say not to alter the existing ground level, or the cover level of any sewer maintenance structure, without its acceptance. Regrading the ground under a deck to move water would be a change of ground level. The guide to building near Sydney Water pipes sets out the rest.
When a Sydney Water stormwater asset is near
Some blocks back onto a stormwater channel or have a large stormwater pipe running nearby. If a Sydney Water stormwater asset is within 10 metres of your site, Sydney Water’s stormwater guide (section 2) requires your building plans to be approved through a water servicing coordinator before any digging, earthworks or building begins. The reason it gives: structures over or close to these assets can worsen flooding and make them harder to maintain.
| Situation | Clearance |
|---|---|
| Building beside the asset | Keep the structure a metre clear of the asset’s outer edge, with nothing built above it. |
| Building over the asset | A metre of clearance to any structure alongside, and 0.6 metres between the asset’s outer edge and the structure above it. |
Building over is the exception. Under section 3 of the guide, Sydney Water will look at it only if all three hold: the new structure stays off any easement and off Sydney Water land, a building already stands over the asset, and there is no other feasible way to develop the block reasonably. Section 5.1 also requires foundations to be designed and certified by a structural engineer, with piers bored rather than driven.
Signs a drain under the deck needs a plumber
In the City of Sydney’s guidance, drainage inspection and maintenance is work for a licensed plumber only. Its signs that a plumber is needed, summarised in its order:
- a sink that spills over
- sewage escaping from an inspection chamber
- a toilet that drains very slowly
- a bad smell that lingers
- dirty water, paper or sewage surfacing on the ground
- a leaking underground pipe that is carrying soil away.
A deck can hide that last one from view. Blockages that keep coming back can point to a damaged pipe, the City adds.
What a council can require
The City of Sydney has power to order an owner to fix broken sewer or stormwater pipes on their property, so the place stays safe and healthy, and it can look into complaints about private drains that owners have left unresolved. The sewer mains themselves are Sydney Water’s. Other councils set their own drainage rules; your council’s stormwater pages are the place to check them.