What Might Be Causing Water to Spontaneously Shoot Out of My Bathroom Sink?

Few things are more surprising — or alarming — than seeing water suddenly shoot out of your bathroom sink. Whether it’s a quick spurt of dirty water or a small flood after using another fixture, it usually points to a blocked or poorly vented drain system.

The good news? It’s fixable — and it’s almost always a sign your plumbing needs some attention, not that it’s broken beyond repair.

Let’s look at why this happens, what’s going on inside your pipes, and what you should do next.

Water shoots up from a blocked drain in a bathroom sink, creating a surprising fountain effect.

1. The Most Common Cause: A Blocked Drain or Waste Pipe

In most Melbourne homes, your bathroom sink, shower, and bath all connect to the same waste pipe. When one of those drains gets partially blocked, air and water pressure build up.

That pressure needs to escape somewhere — and the nearest open outlet (often the sink) becomes the path of least resistance.

You might notice:

• Gurgling sounds in the sink after showering

• Water bubbling or splashing up from the drain

• Slow draining from one or more fixtures

• Unpleasant odours from the sink or floor drain

Typical causes of blockages:

• Hair and soap scum buildup

• Toothpaste residue and bathroom products

• Foreign objects dropped down the drain (earrings, cotton buds, etc.)

• Scale or debris buildup in older pipes

🧰 Plumb Melbourne uses high-pressure water jetting and drain cameras to locate and clear blockages safely — no harsh chemicals or guesswork.

2. Plumbing Vent Problems (Air Pressure Imbalance)

Every plumbing system in Australia must include air vents, usually running through the roof. These vents let air enter the pipes so water can flow freely and prevent pressure build-up.

If a vent becomes blocked by debris, leaves, or even a bird’s nest, air can’t move through the system correctly. The result? Water from another drain (like your shower) can force air back up through your sink trap, causing water to shoot out or gurgle.

Signs of venting issues:

• Gurgling noises after flushing or draining

• Water splashes from one fixture when another is used

• Sewer smells even after cleaning

These are code-compliance issues under the Plumbing Code of Australia (AS/NZS 3500) and should be inspected by a licensed plumber.

3. Shared Waste Line Overload

In multi-storey homes or units, the problem can come from shared or vertical waste lines. When one unit or level discharges water (say, someone upstairs showers), it can push air and wastewater up through another unit’s sink.

This is especially common in:

• Older Melbourne apartment buildings with ageing pipes

• Renovations where bathrooms were added without proper venting

• Properties with long, horizontal pipe runs

A camera inspection is the quickest way to confirm this.

4. Faulty or Missing Sink Trap (U-Bend)

If your sink doesn’t have a proper U-bend or P-trap, water movement in the waste pipe can cause backflow or bubbling. The trap holds water that blocks air and sewer gases — but when it’s missing, damaged, or dry, air pressure can push straight up the pipe.

You might also notice strong odours or gurgling noises.

🪠 If you’re not sure, check under the sink. You should see a curved “U” shape pipe that always holds some water. If not, it’s time to call a plumber.

5. Backflow or Sewer Line Issues

In rarer cases, the issue can be caused by sewer backflow — when water can’t drain into the main sewer due to a blockage further down the line. When this happens, the system “burps” dirty water back into the lowest fixtures, often starting with the bathroom sink or shower.

This can become a health hazard and should be treated as an urgent call-out.

⚠️ If you notice brown or smelly water backing up, stop using water immediately and contact a plumber.

6. Quick Steps You Can Try Before Calling a Plumber

✅ Avoid chemical drain cleaners — they can damage pipes.

✅ Remove and clean the sink plug and visible debris.

✅ Try plunging the sink gently for 10–20 seconds.

✅ Run hot water for a few minutes to clear minor soap scum.

✅ If gurgling continues or water shoots out again, stop and call a licensed plumber.

A plumber in a navy blue hoodie is seen fixing a gold bathroom faucet, surrounded by a variety of tools on a white countertop.

When to Call a Professional

If you’ve noticed any of these signs, the problem won’t fix itself:

• Water bubbling up when other fixtures are used

• Gurgling or air bursts from the sink

• Bad smells or slow draining

• Recent renovations or older plumbing

📞 Call Plumb Melbourne on 0437 296 544 — our licensed plumbers can inspect, clear, and repair drains across South-Eastern and Northern Melbourne, including Glen Iris, Doncaster, Camberwell, and Preston.

We use modern diagnostic tools like drain cameras and water jetters to locate the cause without damaging your fixtures — fast, safe, and compliant with Australian standards.