You're in the shower and the water isn't draining. Or you flush the toilet and the water rises instead of going down. A clogged sewer is frustrating, messy, and can cause significant damage if not addressed quickly. But how do these blockages actually happen?
In this article, we'll discuss the seven most common causes of a clogged sewer. You'll learn how to identify the problem, what you can try yourself, and when it's time to call in a specialist.
1. Grease, oil, and food scraps in the drain
This is by far the most common cause of a clogged sewer for households. Liquid grease seems harmless when you pour it down the sink, but as it cools, it solidifies on the inside of your pipes. Layer by layer, a grease buildup forms, increasingly obstructing wastewater flow.
Food scraps like rice, pasta, and coffee grounds worsen the problem. They clump together with the grease, creating a stubborn blockage that a simple plunger can't clear.
What can you do yourself? Never pour grease or oil down the sink. Let it solidify in an old container and dispose of it with your regular trash. Use a strainer in your drain to catch food scraps.
2. Wipes, wet wipes, and hygiene products
Many people flush wet wipes, tampons, sanitary pads, or even baby wipes down the toilet. Although some packaging claims they are 'flushable,' these products barely dissolve in water. They accumulate in your sewer system and cause stubborn blockages.
Wet wipes are a particularly deceptive culprit. They are sturdier than regular toilet paper and break down much more slowly. When combined with grease and limescale, they form clumps that can completely block your sewer.
Rule of thumb: only the three P's belong in the toilet: pee, poop, and (plain) paper. Everything else should be thrown in the trash.
3. Tree Roots Invading Your Sewer Pipe
Tree roots actively search for water and nutrients. If your sewer pipe has even a small crack or a loose connection, roots will grow inside. Once in the pipe, they continue to grow, trapping debris and eventually blocking the entire flow.
This problem is particularly common in older homes with concrete or clay sewer pipes. Modern PVC pipes are less susceptible, but even they can be penetrated by roots if connections are poorly sealed.
How to spot this? Look for recurring blockages in the same spot, gurgling sounds in multiple drains at once, and a slow-draining pipe that gets progressively worse. Smoke testing or a camera inspection can quickly reveal the problem.
4. Sagging or Break in the Sewer Line
Sewer pipes endure a lot. Ground shifts, heavy traffic above the pipe, freezing and thawing, or simply old age can cause a pipe to sag, crack, or break. Debris collects at the sagging point, leading to a blockage.
If a pipe is broken, soil can enter the line, further worsening the flow. These types of problems cannot be solved with a plunger or high-pressure jet. An inspection and often a sewer repair are needed here.
5. Limescale Buildup and Aging Pipes
In areas with hard water (which includes a large part of the Randstad region), limescale gradually builds up on the inside of your pipes. The diameter of your pipe becomes progressively smaller, making it easier for debris to get stuck and blockages to form more quickly.
With older cast iron or concrete pipes, corrosion also occurs. The inner wall becomes rough, allowing grease and dirt to adhere even more easily. After 30 to 40 years, the original diameter can sometimes be reduced by half. In such cases, sewer renovation can significantly extend the lifespan of your pipe.
6. Incorrectly Connected or Too Narrow Pipes
Sometimes the cause of recurring blockages isn't what you flush down the drain, but rather the installation itself. Pipes that are too narrow, an incorrect slope (the angle at which the pipe runs), or faulty connections can prevent wastewater from draining quickly enough.
This is often seen in renovations where non-certified professionals have modified the sewage system. Also, in apartment complexes where multiple homes are connected to the same main stack pipe, an incorrect connection can cause problems for the entire building. That's why RBNL offers special maintenance programs for Owners' Associations (VvE's) and property managers.
7. Extreme Rainfall and Overload
During heavy rain showers, the sewer system may not be able to handle the volume of water. This is especially true for homes with a combined sewer system, where rainwater and domestic wastewater flow through the same pipe. The sewer becomes overloaded, and water can enter your home through the lowest points (toilets, shower drains, basement drains).
Climate change is exacerbating this problem. The number of extreme downpours in the Netherlands is increasing, while many sewer systems are still designed based on rainfall patterns from decades ago.
How to Identify the Cause?
The symptoms often provide an indication of the cause:
- One drain blocked: likely a local issue (grease, hair, objects) in the drainpipe of that specific point.
- Multiple drains blocked simultaneously: the problem is likely in the main sewer line. Consider tree roots, sagging, or a general blockage.
- Sewer smell in the house: could indicate a partial blockage, a dried-out P-trap (odor seal), or a break in the pipe.
- Gurgling sounds: indicates an obstruction in the drain or a problem with the sewer's ventilation.
- Water in the crawl space or basement: often a sign of a blockage or break in the main line under or next to your home.
When Should You Call a Sewer Specialist?
A simple sink blockage can sometimes be fixed yourself with a plunger or drain cleaner. However, in these situations, it's wise to call a professional:
- The blockage keeps returning, even after you've tried to clear it yourself.
- Multiple drains in your home are blocked at the same time.
- Water is backing up through the toilet, shower, or a drain.
- You smell a sewage odor in your home.
- You suspect tree roots, a sag, or a break in the pipes.
At Rioolbeheer Nederland, we only work with our own certified technicians. We offer fixed, all-inclusive prices with no call-out fees or hidden surcharges. If we don't solve the problem, you don't pay anything. That's our no cure, no pay policy. We are available 24 hours a day, 7 days a week and can usually be with you the same day.
Contact us for quick assistance →
Frequently Asked Questions about a Clogged Sewer
1. How much does it cost to clear a clogged sewer?
At RBNL, you pay a flat rate of €165, all-inclusive. Unclogging the main sewer costs €296. No call-out fees, no hourly rates. View our full price list or contact us for a free consultation.
2. Can I clear a clogged sewer myself?
You can sometimes clear a minor blockage in the sink or toilet with a plunger or drain opener. Do not use aggressive chemical products, as they can damage your pipes. If the blockage keeps returning or multiple drains are clogged, then call in a specialist.
3. How can I prevent a clogged sewer?
Never pour grease or oil down the drain. Only flush the three P's down the toilet. Use strainers in your drains. And have your sewer system preventatively cleaned every two to three years, especially in older homes or if you have trees in your garden.
4. How quickly can a sewer specialist be on site?
At RBNL, we are available 24/7 and can be with you the same day in most cases. In the Randstad region (Amsterdam, Rotterdam, The Hague, Utrecht), our average response time is very short.
5. Does my insurance cover the cost of sewer clearing?
That depends on your policy. Some home insurance policies cover sewer problems resulting from a sudden event. However, clearing costs due to wear and tear or neglected maintenance are usually not covered. Check your policy terms or contact your insurer.
