The most devastating scene during a typhoon: the toilet suddenly sprayed water
Friends who live on the first or second floor in Taipei or New Taipei, if they have experienced heavy rainfall, may have had this devastating experience: An hour or two after the heavy rain, the toilet at home suddenly began to "bubble", and then dirty sewage gushes up from the toilet; the bathroom floor drain also reversed, and the foul-smelling yellow-brown liquid spread to the bathroom floor and even flowed into the living room.
This is not a broken water pipe in your home, but a public drainage pipe network in the entire building or even the entire community. Because the amount of heavy rain exceeds its drainage capacity, the water level in the pipes skyrockets and the pressure backflows. People who live on lower floors bear the brunt of the problem because the drain outlet in your home is closest to the ground and is the easiest outlet for pressure to find.
Physical principles of drainage and backflow
Under normal circumstances, the wastewater in your home flows downward by gravity, flows through the branch pipes on each floor into the drainage riser of the building, and is finally discharged to the underground public sewage sewer. This is a one-way gravity drainage system.
But when the heavy rain outside is too heavy and the drainage volume of public sewers cannot keep up with the inflow, the water level in the sewers will rise. When the water level rises above the level of the drainage outlet on the first floor, the water will in turn "backflow" from the public sewer back into the building's drainage riser. As the water level in the standpipe rises, the drainage branch pipes on the lower floors become pressure relief outlets for this reverse water pressure - your toilet, floor drain, and sink become fountains.
Check valve: the most effective physical line of defense
The most direct way to prevent drainage backflow is to install a "Check Valve" on the drainage pipeline. Some people also call it "Check Valve" or "Check Valve".
The principle of the check valve is very simple: there is a one-way baffle inside. When water flows in the normal direction (away from your home), the current pushes against the flapper to allow water to pass through. When the water flows back (back-flowing in from the outside), the reverse pressure will compress the baffle and lock the pipe.
There are several key points to pay attention to when purchasing a check valve:
- Material: It is recommended to choose white iron or thick-walled PVC material, which is corrosion-resistant.
- With cleaning port: Be sure to choose a model with a "maintenance cleaning port". There will be hair, grease, and various debris in the drain pipe. If the baffle of the check valve is stuck by foreign objects, it will fail. A cleaning port can be opened regularly for cleaning.
- Sealing design: Use silicone soft valve or magnetic flap design, which has better air tightness and can also be used as anti-odor in daily life.
The check valve is not a panacea: understand its limitations
Before installing the check valve, there are a few things that need to be clarified:
- The pipeline cannot be seriously blocked: If your home’s drainage pipe is not very clear (slow drainage, frequent bubbling), after installing a check valve, normal wastewater may not be discharged due to the resistance of the baffle, causing your home to flood. Therefore, before installation, you should ask the master to check the pipeline condition with a high-pressure water jet or pipeline endoscope.
- Excessive water pressure may still cause leaks:The check valve has its upper pressure limit. If the external backflow water pressure exceeds the design range of the check valve, a small amount of leakage may still occur. However, qualified check valves can already block most of the backflow caused by heavy rain in cities.
A once and for all solution: independent drainage pipe modification on the first floor
If your home has a first-floor skylight or a first-floor storefront, and suffers from drainage backflow every typhoon season, the most fundamental solution is to do "independent drainage pipe modification". To put it simply, cut off your home's drainage pipeline from the public drainage riser of the building, open an independent pipeline, and connect it directly to the side ditch or road drainage ditch in front of the door.
The advantage of this is that your home's drainage system is completely unaffected by the building's public pipes. The disadvantage is that the project requires knocking out part of the floor to bury new pipes, and bathroom facilities may be inconvenient for a few days during the construction period. The cost is approximately NT$30,000 to NT$80,000, depending on the length of pipe and floor material. For long-term homeowners, this is an investment that will last a lifetime.
Drainage protection inspection before typhoon
| Check items | How to do |
|---|---|
| Clean all drains | All hair, fallen leaves and debris should be removed from the balcony drain head, roof drainage holes, and bathroom floor drains |
| Check check valve | If it has been installed, open the cleaning port and confirm that the baffle can be opened and closed normally |
| Prepare blocking tools | Prepare some large plastic bags filled with water to make simple sandbags. In an emergency, they can be placed on the ground drain to prevent backflow |
| Prepare pumping tools | If there is a record of flooding in your home, consider preparing a small submersible pump as a backup |
Conclusion: Low floors are not the original sin, but one more step is required
Living on a low floor does not mean you have to suffer every typhoon. Understand the principles of drainage backflow, install appropriate check valves, and keep pipelines open. These small investments can significantly reduce the risk of flooding during heavy rains. If the backflow problem recurs year after year, it’s worth seriously considering independent drainage pipe modifications to solve this perennial pain point once and for all.
Tap water pipeline maintenance and water supply and drainage sanitation and safety standards (2025-2026 Guidelines)
The residential water supply and drainage system is like the blood vessel and metabolic system of the building. According to Taiwan's tap water quality standards and building technical rules for water supply and drainage and sanitary equipment, home water quality and water pressure stability directly affect the water health of the whole family and the lifespan of water equipment. After decades of use, galvanized iron pipes that are common in old apartment buildings in Shuangbei often develop thick rust tumors and biological mud films inside the pipe walls, which not only significantly reduces the water output, but may also release heavy metal impurities, seriously affecting the safety of drinking water.
In terms of hot water systems, old apartments often suffer from insufficient water pressure between floors (dynamic water pressure is less than 0.3 kg/cm²), causing gas water heaters to ignite poorly or bathing to become hot and cold. When installing a pressurizing motor, it is recommended to use a "DC variable frequency constant pressure silent pressurizer" or "electronic flow control pressurizer" with microcomputer chip control to avoid the pipeline water hammer (Water Hammer) effect caused by frequent activation of traditional mechanical pressure switches from damaging old pipe joints. When renovating water supply pipelines, the mainstream industry currently uses SUS304 stainless steel double-crimped coated pipes, which are shock-resistant, temperature-resistant, rust-resistant and corrosion-resistant, and have a service life of more than 30 years.
Key points for daily protection and acceptance of water supply and drainage equipment
- Water meter static leak detection method: When no one in the house is using water and all faucets and toilet inlet valves are closed, observe whether the small red plum blossom pointer in the center of the water meter continues to rotate; if it rotates slightly, it means there is hidden slow seepage in the indoor pipeline or toilet tank.
- Water trap and water seal anti-odor maintenance: There are traps (water seals) inside the bathroom floor drain head and floor drain. If no one uses them for a long time, the isolation effect will be lost due to water evaporation, causing the building's public sewage pipes to cause methane and cockroach pests to enter the room along the pipes. It is recommended to pour 500c.c. of clean water every week to keep the water seal full.
- Regular disassembly and cleaning of the faucet aerator: The aerator filter at the front of the faucet outlet should be removed and cleaned every six months to remove fine sand and calcium carbonate scale deposits carried by the tap water to maintain smooth water flow.
