You're in the shower and the water won't drain. Or you flush the toilet and the water rises instead of going down. A clogged drain is annoying, gross, and if you don't act quickly, it can cause serious damage. But how does a clog like that 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 on your own, and when it’s time to call in a professional.
1. Grease, oil, and food scraps in the drain
This is by far the most common cause of clogged drains in homes. Liquid grease may seem harmless when you pour it down the sink, but as soon as it cools, it solidifies on the inside walls of your pipes. Layer by layer, a grease plug builds up, blocking more and more wastewater.
Food scraps like rice, pasta, and coffee grounds make the problem worse. They clump together with the grease and form a stubborn clog that can’t be cleared with a simple plunger.
What can you do yourself? Never pour grease or oil down the sink. Let it solidify in an old container and throw it away with the general waste. Use a strainer in your drain to catch food scraps.
2. Wipes, moist toilet paper, and hygiene products
Many people flush wet wipes, tampons, sanitary pads, or even baby wipes down the toilet. Although some packaging says “flushable,” these products hardly dissolve in water. They build up in your sewer system and cause stubborn clogs.
Moist toilet paper is a particularly insidious culprit. It’s sturdier than regular toilet paper and breaks down much more slowly. When combined with grease and limescale, it forms clumps that can completely block your sewer.
Rule of thumb: only the three Ps belong in the toilet: pee, poop, and (regular) toilet paper. Everything else goes in the trash.
3. Tree roots invading your sewer pipe
Tree roots actively seek out water and nutrients. If your sewer pipe has even a small crack or loose joint, roots will grow inside it. Once inside the pipe, they continue to grow, trapping debris and eventually blocking the entire flow.
This problem occurs mainly in older homes with sewer pipes made of concrete or fired clay. Modern PVC pipes are less susceptible, but even there, roots can penetrate if the joints are poorly sealed.
How can you tell? Recurring clogs in the same spot, gurgling noises coming from multiple drains at once, and a drain that drains slowly and gets worse over time. Smoke detection or a camera inspection will quickly reveal the problem.
4. Sagging or a break in the sewer line
Sewer pipes have a tough time. Soil subsidence, heavy traffic above the pipes, freezing and thawing, or simply old age can cause a pipe to sag, crack, or break. Debris gets trapped at the sagging point, causing a blockage to build up.
If a pipe is broken, soil can enter the pipe, causing the flow to deteriorate even further. You can’t fix this kind of problem with a plunger or a pressure washer. An inspection—and often a sewer repair —is required.
5. Limescale buildup and pipe deterioration
In areas with hard water (which covers a large part of the Randstad), limescale gradually builds up on the inside of your pipes. The inside diameter of your pipes gradually shrinks, making it easier for debris to get stuck and causing clogs to form more quickly.
With older cast iron or concrete pipes, corrosion is also a factor. The inner wall becomes rough, making it even easier for grease and dirt to accumulate. After 30 to 40 years, the original diameter may have shrunk by half. In such cases, sewer rehabilitation can significantly extend the life of your pipe.
6. Incorrectly connected or too narrow pipes
Sometimes the cause of recurring clogs isn’t what you flush down the drain, but the plumbing itself. Pipes that are too narrow, an incorrect slope (the angle at which the pipe runs), or faulty connections prevent wastewater from draining quickly enough.
This is a common occurrence during renovations where uncertified contractors have modified the sewer system. In apartment complexes where multiple units are connected to the same riser, an incorrect connection can also cause problems for the entire building. That is why RBNL offers special maintenance programs for homeowners’ associations and property managers.
7. Extreme rainfall and overload
During heavy rainstorms, the sewer system cannot 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 pipes. The sewer system becomes overloaded, and water can enter your home through the lowest points (toilets, shower drains, basement drains).
Climate change is exacerbating this problem. The frequency of extreme downpours in the Netherlands is increasing, while many sewer systems are still designed to handle the rainfall patterns of decades ago.
How can you tell what the cause is?
The symptoms often provide a clue as to the cause:
- One drain is clogged: this is likely a localized issue (grease, hair, or foreign objects) in the drain pipe at that specific point.
- If multiple drains are clogged at the same time, the problem is likely in the main sewer line. Possible causes include tree roots, subsidence, or a general blockage.
- A sewer smell in the house: this could indicate a partial blockage, a dry trap, or a break in the pipe.
- Gurgling noises: indicate a blockage in the drain or a problem with the sewer vent.
- Water in the crawl space or basement: often a sign of a blockage or a break in the main water line under or next to your home.
When should you call a sewer specialist?
You can sometimes clear a simple sink clog yourself using a plunger. But in these situations, it’s best to call a professional:
- The clog keeps coming back, even after I've unclogged it myself
- Several drains in the house are clogged at the same time
- Water is backing up through the toilet, the shower, or a drain
- You can smell a sewer odor in your home
- You suspect tree roots, a sinkhole, or a crack
At Rioolbeheer Nederland, we work exclusively with our own certified technicians. We offer fixed, all-inclusive prices with no call-out fees or hidden charges. If we can’t fix the problem, you don’t pay a thing. That’s our “no cure, no pay” principle. We’re available 24 hours a day, 7 days a week, and can usually be at your location the same day.
Contact us for quick assistance →
Frequently Asked Questions About a Clogged Sewer
1. How much does it cost to unclog a sewer line?
At RBNL, you pay a flat rate starting at €165, all-inclusive. No call-out fees, no hourly rates. View our full price list or contact us for a free consultation.
2. Can I unclog a drain myself?
A minor clog in the sink or toilet can sometimes be cleared with a plunger. Do not use harsh chemical drain cleaners, as they can damage your pipes. Is the clog recurring, or are multiple drains clogged? If so, call a professional.
3. How can I prevent a clogged sewer?
Never pour grease or oil down the drain. Only flush the three Ps down the toilet. Use strainers in your drains. And have your sewer lines cleaned preventively once every two to three years, especially in older homes or if you have trees in your yard.
4. How quickly can a sewer specialist arrive on site?
At RBNL, we’re available 24/7 and can usually be with you the same day. In the Randstad (Amsterdam, Rotterdam, The Hague, Utrecht), our average response time is very short.
5. Does my insurance cover the cost of unclogging a drain?
That depends on your policy. Some home insurance policies cover sewer problems caused by a sudden event. Costs for unclogging drains due to wear and tear or overdue maintenance are usually not covered. Check your policy terms and conditions or contact your insurer.
