If you noticed your drains backing up the day after a Melbourne storm, you are not alone. Heavy rain is the single biggest predictor of blocked drain callouts. Here is what is actually happening.
Stormwater overload
Melbourne's stormwater system was designed for the rainfall patterns of decades past. Rainfall events are larger and more concentrated now. When stormwater pipes fill faster than they can drain, water backs up through any low point - your stormwater pit, the gully trap, even floor drains.
Cross-connections between systems
In older parts of Melbourne (inner suburbs especially), stormwater and sewer systems are sometimes inadvertently connected, either at the property boundary or in old shared lines. Heavy rain in the stormwater system can push sewage backwards through your fixtures. This is rare but it happens, and it is unpleasant.
Roof gutter overflow
Blocked gutters and downpipes overflow during storms. Water then runs down walls and pools at the base of the house, which is where stormwater connections often are. The result is water entering pipes from the wrong direction, picking up leaves and debris, and creating new blockages.
Tree root activity
Tree roots in your sewer line are already partially blocking water flow. In dry weather, the system works because the trickle of water can squeeze past. After heavy rain, when the drainage load doubles, the partial blockage becomes a full one.
What you can do before storm season
Clear your gutters and downpipes. Sounds obvious but most Melbourne homes do not do this annually. October before summer storms is the right time.
Get your stormwater pit checked. Lift the lid and clear out any leaves, soil buildup, or debris. Run a garden hose down it to confirm water flows freely.
If you have had any drain issues in the past year, get a CCTV inspection done in a dry month. Fixing partial blockages before they become full ones saves a much bigger callout during the storm.
What to do during a storm backup
Stop using all water fixtures immediately. Continued use makes the backup worse.
Call a plumber. Most Melbourne plumbers handle storm emergencies but expect longer wait times because callouts spike.
If sewage is coming up, do not try to plunge or flush. Wait for the plumber.