There’s nothing quite like the smell of fresh rain, unless your house smells like a sewer. If you’ve ever stepped into your home after heavy rain and been hit with a foul smell that resembles rotten eggs or sewage gases, you’re not alone. Many homeowners across Perth and Mandurah report a sewer smell after rain, especially around the bathroom, shower, floor drain, or laundry.
This article explores why that happens, what it could mean for your plumbing system, and how a professional plumber from Swan’s Professional Plumbing can help prevent things from getting worse.
Smell sewage after it has rained? Contact our team of local Perth Plumbers today!
Common Reasons for a Sewage Smell After Rain
There are a few common reasons why sewer gas or a pungent odour finds its way into your home when it rains. While some causes are minor, others can signal damage in your sewer system or septic tank. Here’s what might be happening:
Dried Out Water Barriers (P-Traps)
Every sink, shower, and floor drain in your home has a p-trap, a curved section of pipe designed to hold a small amount of cold water or hot water to form a water barrier. This barrier blocks sewer gases from escaping back into your home.
If you’ve got a guest bathroom, floor drain, or shower drain you haven’t used in a while, the water can evaporate. That’s when the sewer gas smell enters the room.
Quick fix: Pour a cup of cold water down any infrequently used drains. For a longer-term solution, you could pour a small amount of mineral oil in the trap to slow evaporation.
Blocked or Clogged Drains
A clogged drain doesn’t just cause slow water flow. It can also trap organic material (like hair, soap scum, and human waste) that breaks down and releases a foul odour. After rain, water pressure changes and extra moisture can push that bad smell into your home, especially if multiple plumbing fixtures are backing up.
If your drainage system is frequently slow or smelly, check out our drain repair and clearing services.
Sewage Backup After Rain
Heavy rain can overwhelm Perth’s older sewer systems, especially if they’re shared or semi-public. When that happens, stormwater and sewage may mix and create pressure that forces sewage gases or even wastewater back into your property.
This often leads to:
- Gurgling noises from the toilet or floor drain
- Water pooling near outdoor sewer lines
- Strong sewer smell throughout the house
This situation requires urgent attention. Contact our team for professional inspections and repairs.
Cracked Pipes or Broken Pipe Joints
Over time, cracked pipes or broken pipe connections underground can release sewer gas leakage into the soil. After rain, moisture helps carry these odours up and into your home. The smell is strongest near floor-level fixtures or where the pipe damage is closest to the surface.
This is especially common if:
- Tree roots are nearby
- You’ve had soil movement
- Your property uses older materials like clay pipe
Our licensed plumbers use CCTV drain cameras to identify faults like these without tearing up your garden. Learn more about our leak detection services.
Vent Pipe Problems
Your home’s vent pipe system allows air to enter your plumbing system, helping water flow properly and preventing sewer gas from building up. Sometimes the vent can be:
- Blocked by leaves or debris
- Damaged during roof work
- Incorrectly sized or installed
In these cases, it can trap air and force gases back into your home, especially during a storm when outside air pressure changes rapidly.
Issues With Septic Systems
If you’re not connected to mains sewer and instead have a septic tank, a sewage smell after rain may mean the system is full, has poor drainage, or that the septic system is failing altogether. Heavy rain can saturate the drain field, making it impossible for wastewater to filter properly, resulting in a sewage backup or lingering foul smell around the house.
If you are located in Perth, Mandurah, or the outer suburbs, we can assist you with inspecting and servicing on-site systems. Reach out to Swan’s for tailored support.
Poor Plumbing Design or Renovation Mistakes
Sometimes, the issue is caused by DIY or unlicensed work that doesn’t follow plumbing code. Common mistakes include:
- Improperly installed or missing venting
- Fixtures with no p-trap
- Shared drain lines that shouldn’t be connected
These setups can result in sewer gas present in parts of the home every time it rains.
If your home has had recent renovations, especially in bathrooms or laundries, and now the house smells like sewage after rain, we recommend booking a system check.
Our team can redesign or upgrade your plumbing to meet code and eliminate recurring issues.
Is Sewer Gas Dangerous?
Yes. While a one-off whiff of a sewer gas smell might be unpleasant, consistent exposure isn’t safe. Sewage gases can include:
- Methane (explosive in large amounts)
- Hydrogen sulphide (toxic and smells like rotten eggs)
- Ammonia (irritant)
These gases can cause headaches, nausea, eye irritation, or worse. If you experience that your home often has a sewage smell after rain and is strong enough to make you feel unwell, call a professional plumber immediately.
What You Can Do to Reduce Smells
Here are a few practical things you can do while waiting for repairs or if the issue is minor:
- Flush unused drains weekly with hot water
- Add chlorine bleach to kill odour-causing bacteria in traps (use cautiously)
- Pour mineral oil into unused traps to reduce evaporation
- Inspect external vents and clear any visible debris
- Use drain covers or plugs to block smells temporarily
Still smelling something off? We’re ready to help.
How Swan’s Professional Plumbing Can Help
At Swan’s Professional Plumbing, we don’t just mask the problem; we find it and fix it. With years of experience across Perth and Mandurah, we understand how heavy rain interacts with your home’s drainage system and plumbing infrastructure.
Our services include:
- Fixing drains
- Leak detections
- Backflow prevention and testing
- Full plumbing system repairs for broken or cracked infrastructure
No job is too big or too small. Whether you need to replace pipes, clear a clogged drain, or track down a mystery odour, we’ve got the tools and know-how.
