Stormwater or Wastewater? How to Tell Which Drain Is Blocked in Dunedin

When water starts backing up on your property, the first question we ask is which system it is coming from. Every Dunedin home has two separate drainage networks: stormwater, which carries rain from the roof, paths and driveway, and wastewater, which carries everything from the toilets, showers, sinks and laundry. They block for different reasons, they need different fixes, and in some cases responsibility for the repair sits with someone other than you.

Stormwater and wastewater: what each one does

Stormwater drains collect rainwater from your downpipes, yard grates and driveway channels and carry it away to the street kerb, a soak pit or the council stormwater network. In the older parts of Dunedin some of these are connected to combined systems that also carry wastewater, which is one reason heavy rain can cause problems in the sewer network.

Wastewater drains, also called sewer or foul drains, take used water from inside the house. They run from each fixture to a gully trap outside, then along the main private drain to the point where it connects to the council sewer. Because they carry solids, fat and paper, they block more easily than stormwater lines.

The Dunedin City Council wastewater pages explain how the public network works and what the council looks after. The short version is that the council maintains the public mains, while the pipes on your property are yours.

How to tell which one is blocked

Look at where the water is appearing and when.

• Water overflowing from a gully trap (the small open grate near the outside wall of the house, usually below the kitchen or bathroom) is wastewater. If it happens when you run a tap or flush, the private sewer line is blocked.
• Toilets that are slow to flush, gurgling or rising, especially when another fixture is used, point to the wastewater line.
• Water pooling around a yard grate, at the base of a downpipe or across the lawn during or after rain, with the house plumbing working normally, is a stormwater problem.
• A driveway channel or kerb outlet that fills and will not drain is stormwater.
• Overflow that smells is almost always wastewater. Stormwater backing up usually smells of little more than wet soil.

If both systems are playing up at once, or the problem only appears in heavy rain but affects the toilets, the two may be cross-connected somewhere, which is more common in older Dunedin properties than people expect. A CCTV drain inspection is the quickest way to map what is actually connected to what.

Common causes of a blocked stormwater drain

• Leaves, moss and roof grit washed down the downpipes, particularly in autumn and after a storm.
• Silt and soil washed in from gardens and unsealed driveways.
• Tree roots in older earthenware or concrete lines.
• Crushed or displaced pipe where vehicles drive over shallow lines.
• A soak pit that has silted up and can no longer take the flow.

Stormwater blockages often build slowly and only show themselves in a downpour, which is precisely when you least want to be dealing with them. Clearing them is usually straightforward with high-pressure water blasting, which flushes the silt and debris through to the outlet.

Common causes of a blocked wastewater drain

• Fat, oil and grease poured down the kitchen sink, which sets hard as it cools in the pipe.
• Wet wipes, sanitary products and paper towels, none of which break down the way toilet paper does.
• Tree roots getting in through open joints.
• Broken, sagged or collapsed sections of old pipe.
• Build-up in a gully trap or a blocked vent letting the line airlock.

A single blockage can generally be cleared the same day. If the same wastewater line keeps blocking, the camera will usually show a structural cause such as roots or a broken pipe, and at that point a repair through excavation and drainlaying is the way to stop it recurring.

Who is responsible for the repair?

As a general rule, the property owner is responsible for the private drains within the property, and the council is responsible for the public mains and the connection point. Where exactly one ends and the other begins varies from property to property, and on older sections shared private drains that cross more than one property are not unusual. If a CCTV inspection shows the fault sits at or beyond your boundary, we will tell you, because that changes who should be paying for the fix. Tenants should report drainage problems to their landlord or property manager rather than arranging repairs themselves.

What to do right now

• Stop using water inside if wastewater is overflowing. Every flush adds to the overflow.
• Keep children and pets away from any sewage overflow and hose down the area once the drain is clear.
• If stormwater is pooling against the house, clear the yard grate of leaves and check the downpipe outlets, which fixes a surprising number of rain-day problems.
• If in doubt, call. We can usually tell you over the phone which system is involved and what the next step should be.

Drain Clearing Otago clears both stormwater and wastewater blockages across Dunedin and Otago, with a 24-hour emergency service for the ones that cannot wait. Call 027 474 2274 or get in touch online.