Stormwater: where the rain goes after your roof

02-A · The journey

From your roof to the river, in five pits

In a city, hard surfaces like roofs, roads and footpaths stop rain soaking into the ground, and the run-off they create is stormwater. This is the route it takes, and whose hands it passes through.

1. Your roof

   Gutters and downpipes

   Downpipes are connected to the roof gutters, and as a property owner you have a role in maintaining the stormwater downpipes on your property. The NSW SES asks householders to clear gutters, downpipes and drains regularly: blockages can trap water and make it overflow under the eaves into the roof cavity.

2. Your block

   The property drain

   From the downpipes, stormwater often flows through property drains to the street. It belongs in its own pipes: wastewater and stormwater are carried in two separate sets of pipes and plumbing systems.

3. The council

   The kerb and gutter

   Street gutters are operated by local councils. In Liverpool, the council’s water quality strategy includes water quality treatment systems installed as part of road, footpath and park upgrades.

4. Council or Sydney Water

   Channels, pipes and basins

   Gutters may connect to large channels, pipes and creeks. Sydney Water provides stormwater services mainly in south and south-west Sydney, and works with councils elsewhere; its stormwater catchment map shows whether it manages your local stormwater.

5. The waterways

   Creeks and two rivers

   The Georges and Nepean rivers both run through the Liverpool area, with many creeks feeding them. Whatever the stormwater has picked up, from litter to oil and grease from cars, travels with it.

02-B · Two pipes

Why rain belongs in its own pipes

When a stormwater pipe is connected incorrectly, or rain can get into the wastewater system, it can cause overflows that affect the community and the environment. Sydney Water lists stormwater overloading its wastewater network in heavy rain among the causes of blockages.

Its overflows page lists the ways rain gets in: cracks in pipes, bad joints where pipes meet, gaps around maintenance hole lids, and stormwater pipes plumbed straight into the system. It names heavy rain as a common cause of wastewater overflows.

Connections can be checked two ways, Sydney Water says: smoke testing, where a small amount of non-hazardous smoke is pumped into wastewater pipes to find leaks and wrong connections, and a visual check of downpipe connections and outdoor drains.

02-C · Liverpool’s part

What the council builds for stormwater

Liverpool City Council says its waterways are under pressure from past and present development, and that the growth expected in the west of the area will produce significant pollution loads. Its Water Quality Management Strategy includes a gross pollutant trap master plan, a guideline for water sensitive urban design in new development, treatment systems built into road, footpath and park upgrades, and riparian zone management.

Some of it you can see from the footpath. The council describes rain gardens as porous gardens that capture run-off from roofs, driveways, paths and car parks and let it soak through into an underground stormwater system, and asks residents to report a distressed one through the Snap Send Solve app. In Austral and Leppington North, it says it will provide trunk drainage and regional detention basins with biofilters, plus streetscape rain gardens on new roads.

02-D · Keeping it clean

What reaches the gutter reaches the creek

Stormwater carries whatever collects on hard surfaces: litter, oil and grease from cars, dirt and leaves, animal droppings, and chemicals from washing a car on the driveway. Sydney Water’s list of what a household can do:

• put rubbish in the bin;
• wash the car on the grass, so detergent soaks into the soil instead of the drain;
• 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;
• pick up after your pet and bin it;
• take chemicals, pesticides, paints and oils to the council’s chemical clean-out services.

02-E · Stay out

The grate is a lid, not a door

Stormwater systems include open channels, drains, tunnels and maintenance holes, and Sydney Water says only authorised crews can enter them safely. Water can rise fast and unexpectedly, even when it isn’t raining; shallow flowing water can knock you over; and stormwater may carry chemicals and disease-causing bacteria.

Its education pages add one more: leave the stormwater grates by footpaths and roads alone, even if something falls through. They can be very heavy.