Stormwater vs Sewer Drains: How to Tell the Difference

If you’re dealing with slow drainage, bad smells, or water backing up, one of the first questions we ask is whether the issue is in the stormwater drain or the sewer drain.

They do very different jobs — and confusing the two can lead to wasted time, incorrect repairs, and ongoing problems.

This guide explains how to tell the difference and why it matters.

What Is a Stormwater Drain?

Stormwater drains are designed to carry rainwater only.

They collect water from:

• Roof gutters

• Downpipes

• Surface drains

• Driveway and yard pits

Stormwater usually discharges to:

• The street kerb

• A legal point of discharge

• A soakwell or drainage system

Stormwater drains should never carry waste water.

What Is a Sewer Drain?

Sewer drains carry wastewater from inside the building.

They connect to:

• Toilets

• Sinks and basins

• Showers

• Dishwashers and washing machines

Sewer drains connect to the main sewer system, not the street gutter.

Key Differences at a Glance

Stormwater drains:

• Carry rainwater only

• Usually run from roof or surface drains

• Often discharge to the street

• Problems show up during or after rain

Sewer drains:

• Carry wastewater from inside the home

• Connected to toilets and fixtures

• Always flowing (not rain dependent)

• Problems usually involve smells or backups

How to Tell Which Drain You’re Dealing With

1. Look at What’s Connected

If the drain connects to:

• Gutters or downpipes → Stormwater

• Toilets, sinks, showers → Sewer

This is the most reliable indicator.

2. Smell the Drain

• Strong sewage smell → Sewer drain

• No smell or earthy smell → Stormwater

Stormwater drains should not smell like sewage.

3. Check When the Problem Occurs

• Issues only during heavy rain → Stormwater

• Issues all the time or during use → Sewer

Timing is often the biggest clue.

4. Observe the Discharge Point

• Water flowing to the street kerb → Stormwater

• No visible discharge point → Likely sewer

In some properties, this may not be visible without inspection.

Why It’s Important to Know the Difference

Treating a sewer issue like stormwater — or vice versa — can:

• Delay the correct fix

• Increase repair costs

• Cause repeat blockages

• Lead to property damage

In some cases, incorrectly connected drains can also cause compliance issues.

Common Problems We Se

Stormwater issues:

• Blocked or collapsed pipes

• Tree root intrusion

• Inadequate fall

• Undersized drainage for heavy rain

Sewer issues:

• Grease and waste build-up

• Tree roots

• Pipe damage or misalignment

• Incorrect fixture connections

When a CCTV Drain Inspection Helps

If it’s unclear which system is causing the issue, a CCTV drain inspection can:

• Confirm whether the pipe is stormwater or sewer

• Identify blockages, damage, or misconnections

• Prevent unnecessary excavation

This is often the fastest way to get a clear answer.

Not Sure Which Drain Is Causing the Problem?

If you’re unsure whether you’re dealing with stormwater or sewer drainage, we can help identify the issue and recommend the correct solution.

👉 Book a drain inspection

We’ll assess the system, confirm the cause, and talk you through the next steps.