Sydney yards flood in heavy rain when stormwater can’t get away fast enough. The usual causes are blocked gutters, downpipes, pits or kerb outlets, tree roots or broken pipes, poor grading and clay soils that don’t absorb water. Most problems are fixed by clearing and jetting the line, repairing damaged pipes, or adding pits and subsoil drains. You maintain the pipes on your property; council maintains the street drains.
Sydney gets a lot of rain in a short time. The city averages 1,213 mm a year at Observatory Hill, and in March 2022 it recorded 537 mm in a single month, the wettest March on record (Bureau of Meteorology). When that much water falls in hours rather than weeks, any weak point in a home’s stormwater system shows up as overflowing gutters, ponding lawns, wet subfloors and water at the back door.
This guide explains how home stormwater systems work, why they fail in heavy rain, how to diagnose the problem, and which fixes a homeowner can do versus a licensed plumber. It also covers who is responsible for pipes, pits and runoff from neighbours under NSW council rules. The licensed drainage team at Radiant Plumbing wrote it from the stormwater jobs we attend across Sydney after every big storm.
Water pooling every time it rains? Radiant Plumbing can find the cause with a camera and fix it properly. Call (02) 8866 1322.
How Does a Home Stormwater System Work?
A home stormwater system collects rain from the roof and paved areas and carries it by gravity to a legal point of discharge. It is separate from the sewer.
- Roof: gutters collect rain and feed downpipes.
- Downpipes: carry water down to underground stormwater pipes, usually 90 to 100 mm PVC.
- Pits: grated surface pits collect water from paving and lawns; inspection pits give access to the pipes.
- Subsoil (ag) drains: slotted pipes in gravel collect groundwater behind retaining walls and under wet areas.
- Discharge point: the water must leave the property at a legal point of discharge.
Under AS/NZS 3500.3, legal points of discharge include the council kerb and gutter, an inter-allotment drainage easement, an approved on-site disposal system such as an absorption trench, or a council drainage easement (Hornsby Shire Council). Many newer homes also have a rainwater tank or an on-site detention (OSD) tank that holds water back during storms.
What Are the Signs of a Stormwater Drainage Problem?
The clearest sign is water that stays where it shouldn’t after rain. Look for:
- gutters overflowing even when they look clean
- downpipes leaking at the joints or bubbling at the base
- surface pits filling and overflowing during rain
- water ponding on the lawn or paving for hours afterwards
- a soggy patch along the line of an underground pipe
- water at the back door, garage or in the subfloor
- erosion, sinkholes or washed-out mulch near a pit
- no water coming out of the kerb outlet during rain
Damp patches on internal walls after rain can also come from a plumbing leak rather than stormwater. Our guide to the warning signs of a burst pipe in a wall helps you tell the difference.
What Causes Stormwater Drainage Problems in Sydney?
Most stormwater problems in Sydney come from six causes.
Blocked Gutters and Downpipes
Leaves, seed pods and sludge block gutters and downpipes, so water spills over the gutter edge and pours down beside the house. Gutters that are undersized for the roof area, or have too few downpipes, overflow even when clean.
Blocked Pits and Kerb Outlets
Silt, leaves and mulch wash into surface pits and settle in the pipes. A blocked outlet at the kerb backs water up through the whole system, so pits overflow even though the pipes are fine.
Tree Roots and Broken Pipes
Roots enter stormwater pipes at joints and cracks, especially in older earthenware lines. Vehicles, ground movement and building work can crush or disconnect shallow pipes. A broken pipe leaks into the soil, causing soggy patches and, over time, subsidence.
Poor Fall and Low Spots
Stormwater relies on gravity. Pipes need a steady fall, typically about 1 in 100 for common house pipe sizes, to keep water and silt moving. Pipes laid flat, with a reverse fall or a sag, hold water and silt until they block. Yards graded toward the house send surface water to the back door.
Clay Soils and Seepage
Reactive clay soils, common across Western Sydney, absorb water slowly, so lawns pond after heavy rain. On sloping blocks, especially sandstone areas on the North Shore and in the Eastern Suburbs, groundwater seeps through the soil and appears behind retaining walls and in subfloors.
Charged Systems That Never Drain
In a charged (wet) system, downpipes feed an underground pipe that rises to an outlet, so water sits in the pipe permanently. Silt settles in that standing water, and the system slowly loses capacity until downpipes back up in a storm.
How Do You Work Out What’s Causing the Problem?
Matching the symptom to the likely cause narrows the fix quickly.
| Symptom | Likely cause | Usual fix | Who does it |
| Gutter overflows along its length | Blocked gutter or downpipe, or too few downpipes | Clean gutters; add a downpipe or larger gutter | Homeowner (cleaning); plumber (new downpipe) |
| Downpipe bubbles or overflows at the base | Blocked or broken underground pipe | Jet the line; camera inspection | Plumber |
| Pits overflow in rain | Silt in pits or pipes; blocked kerb outlet | Clean pits; jet to the outlet | Homeowner (pit grate); plumber (jetting) |
| Soggy strip along a pipe line | Broken or root-damaged pipe | Camera, then reline or replace | Plumber |
| Lawn ponds for hours | Clay soil, poor grading | Surface pit, ag drain or regrading | Plumber or landscaper |
| Water behind a retaining wall or in the subfloor | Seepage, missing or blocked ag drain | Clear or install an ag drain | Plumber |
| No flow at the kerb outlet | Blocked or crushed outlet pipe | Jet or repair the outlet | Plumber |
A camera inspection confirms the cause when the problem is underground. Our guide to CCTV drain inspection costs in Sydney explains prices and what the report should show.
What Can You Fix Yourself?
Homeowners can safely do the routine maintenance that prevents most stormwater problems:
- clean gutters at least twice a year, and before storm season
- fit leaf guards or rainheads to reduce leaves in downpipes
- lift surface pit grates and scoop out leaves and silt
- keep mulch, soil and lawn clippings away from pits and grates
- check the kerb outlet flows during rain and isn’t covered by grass
- make sure downpipes are connected to the underground pipe, not spilling onto the ground
Work safely. Use a stable ladder or a gutter cleaning service for two-storey roofs, lift heavy pit lids with a proper lifter, and leave council kerb inlets and street pits to council.
How Do Plumbers Fix Stormwater Problems?
Plumbers fix stormwater problems by clearing, repairing or redesigning the part of the system that has failed:
- High-pressure jetting removes silt, leaves and roots from pipes and outlets.
- CCTV inspection finds broken, crushed or sagging sections and their exact location.
- Pipe relining seals cracked or root-damaged pipes from the inside, without digging up paving.
- Excavation and replacement fixes collapsed pipes, reverse falls and sags.
- New surface pits catch water where the yard ponds.
- Agricultural (ag) drains collect seepage behind retaining walls and under wet lawns.
- Extra downpipes or larger gutters stop roof overflow.
- Converting a charged system or adding a silt pit reduces build-up.
- Absorption trenches or OSD tanks are used where council requires on-site disposal or detention.
Some work, such as connecting to council’s kerb, building over a drainage easement or changing an approved system, needs council approval. A plumber will tell you when it does. Our guide to pipe relining costs in Sydney covers repairs for damaged pipes without digging.
How Much Does It Cost To Fix Stormwater Drainage in Sydney?
Clearing a blocked stormwater line in Sydney usually costs $250 to $600, more if pits are full of silt or roots have got in. A stormwater camera inspection costs about $250 to $450. Relining a damaged section costs $450 to $800 a metre plus setup, or $2,500 to $5,000 for a patch. New pits, ag drains and regrading are quoted after a site visit, because the price depends on length, depth, access and what has to be dug up and reinstated. Our guide to drain cleaning costs in Sydney lists clearing prices in detail.
Who Is Responsible for Stormwater Drains in NSW?
Property owners are responsible for the stormwater system on their land, including the outlet at the kerb. NSW councils publish the same basic rules:
| Who | Responsible for |
| Property owner | Gutters, downpipes, pipes, pits, ag drains and the outlet to the kerb on their property |
| Owners sharing an easement | Inter-allotment drainage pipes in a private easement, shared between the benefiting properties |
| Council | Street kerb and gutter, street pits and council-controlled easements and reserves |
| Sydney Water | The sewer junction and mains, not stormwater on your property (13 20 90) |
Owners must keep their system working and drain to a legal point of discharge (Hornsby Shire Council; The Hills Shire Council). Report blocked council infrastructure to your council, and call a plumber for anything on your own land.
What If a Neighbour’s Stormwater Floods Your Yard?
In NSW, a lower property must accept the natural flow of water from higher land. A neighbour must not divert, redirect or concentrate flow onto your property, for example with a pipe, a new paved area or a solid wall (Hornsby Shire Council; The Hills Shire Council). Councils usually only investigate when man-made works have concentrated the flow, or defective roof drainage is the cause.
Talk to your neighbour first. If that doesn’t resolve it, LawAccess NSW (1300 888 529) can explain your options. A plumber can also manage the natural flow on your side with pits, ag drains or a dish drain.
Why Must Stormwater Stay Out of the Sewer?
Stormwater must never be connected to the sewer. Hornsby Shire Council states that “stormwater pipes are not allowed to be connected to the sewerage system”. Rainwater entering the sewer overloads it in storms and causes overflows of diluted raw sewage into homes and waterways.
Two things let stormwater in: an illegal connection, such as a downpipe plumbed into a sewer pipe, and an overflow relief gully that sits too low, so rain runs straight into it. A plumber can raise the gully or lower the ground around it. If sewage comes up through your gully during rain, the problem is in the sewer, not the stormwater. Our guide to the common causes of blocked drains in Sydney covers sewer blockages.
What Should You Do if Water Is Coming Inside?
If stormwater is coming inside, protect people first, then the house:
- Stay out of floodwater and never drive or walk through it. For a flood emergency, call the SES on 132 500.
- Switch off power at the switchboard if water is near outlets or appliances, only if it is safe to reach.
- Move valuables and electrical items off the floor.
- Clear the nearest surface grate or downpipe outlet if it is safe to do so.
- Photograph the water and damage for insurance.
- Call a plumber once the rain eases to find and fix the cause.
If the water is from a burst or leaking pipe rather than rain, turn off the water at the meter. Our guide to emergency water leak repair explains the next steps.
How Can You Prevent Stormwater Problems Before the Next Storm?
A short routine before storm season prevents most stormwater call-outs:
| When | What to check |
| Before storm season (spring) | Clean gutters and downpipes; clear pit grates; check the kerb outlet |
| Every few months | Lift pit grates and remove silt and leaves |
| After heavy rain | Walk the yard: look for ponding, soggy strips and overflowing pits |
| Every few years | Camera inspection if trees grow near the lines or problems repeat |
If you’re buying a home on a sloping block or with big trees, ask for the stormwater lines to be checked as part of a home plumbing inspection.
Stormwater Drainage FAQs
Why does my backyard flood when it rains?
Usually because water can’t get away fast enough: blocked pits or outlets, broken pipes, poor grading or clay soil that drains slowly.
Who is responsible for blocked stormwater drains?
The property owner is responsible for pipes, pits and the kerb outlet on their land. Council is responsible for street drains and council easements.
What is a legal point of discharge?
The approved place your stormwater must go, such as the council kerb and gutter, an inter-allotment drainage easement or an approved on-site system.
Can I connect my downpipes to the sewer?
No. Stormwater must not be connected to the sewer in NSW. It overloads the sewer and causes overflows.
How much does it cost to clear a stormwater drain?
Usually $250 to $600 in Sydney, more if pits are full of silt or roots have got in.
What can I do about my neighbour’s stormwater?
You must accept natural flow from higher land, but a neighbour must not divert or concentrate water onto your property. Talk to them first; LawAccess NSW can advise if that fails.
Get Your Stormwater Fixed Properly With Radiant Plumbing
Stormwater problems in Sydney come down to water that can’t get away fast enough: blocked gutters, pits and outlets, damaged pipes, poor fall and slow-draining soils. Clean what you can safely reach, then have a plumber find and fix the cause before the next big storm.
Radiant Plumbing clears, inspects and repairs stormwater systems across Sydney, from the Inner West and Eastern Suburbs to the North Shore, Hills District, Western Sydney and St George. If water is coming into your home now, call our emergency plumbing team.
Book a stormwater check: call Radiant Plumbing on (02) 8866 1322, request a quote online, or see our blocked drain services.
