In this post, we highlight a key component for protecting against water from the sewer: the backwater valve. You'll learn how it works, how to retrofit a backwater valve in your sewer line, and why reliable protection requires a comprehensive backwater protection .
The correct technical term: While "backwater valve" is the more common everyday term, the technically correct term is actually "backflow preventer". Strictly speaking, a backwater valve is only a mechanical part of a backflow preventer. For readability, we use the familiar everyday term "backwater valve", but we always mean the professional, standard-compliant complete backflow preventer unit.
Backwater Valve Explained Briefly
- Protective Function: A backwater valve is designed to prevent wastewater from flowing back into the house sewer and emerging from drains below the backwater level when public sewer systems are overloaded (e.g., due to heavy rain, flooding, or blockages).
- Easy Retrofitting: Retrofitting a backwater valve in the sewer line is feasible for most properties without extensive construction work.
- Comprehensive Protection: The backwater valve is always only one part of the solution. Reliable protection is only achieved through a well-thought-out backwater protection concept and its implementation.
- Models: Mechanical valves are used for faeces-free wastewater (greywater). If toilets are connected to the line, an electric motor-driven backwater valve is legally required.
- Manufacturers & Installation: Models from reputable brands (such as Kessel, HL, or ACO) must be installed by specialist companies (like DerKanal) – usually in an inspection shaft or directly in the basement.
- Maintenance: Without regular maintenance, the function of the backwater valve or backflow protection is not guaranteed. In an emergency, this can even lead to your insurance coverage becoming void.
When is a backwater valve advisable?
First and foremost: A single backwater valve or backflow prevention device is never sufficient for reliable protection against flooding – a comprehensive backflow protection concept is always required.
Backwater valves must not be used in multi-family homes and only for drainage pipes serving secondary uses!
As previously mentioned, components of such a concept include backwater valves or backflow prevention devices, as well as sealing measures and pumping stations.
In principle, according to current standards, it is assumed that drainage systems, at least in new constructions, are built to be backflow-proof. In some cases, proper backflow protection is also a mandatory requirement in building insurance policies.
In most cases, this backflow level corresponds to the street or sidewalk level directly in front of your house.
Typical examples where action is required:
- Basement rooms: Open floor drains in the boiler room, laundry room, or storage room.
- Basement living areas (garden level): Sinks, showers, or toilets located below street level.
- Utility connections: Lower-lying connections for the washing machine or a utility sink in the basement.
The issue becomes particularly critical when your property is connected to a combined sewer system. Here, rainwater and wastewater flow through the same pipe. If heavy downpours overload the public sewer, this mixture inevitably pushes back into unprotected house connections.
Retrofitting a backwater valve in the sewer
Many homeowners ask themselves: Can a backwater valve be retrofitted in the sewer of an existing house? The clear answer is: Yes, in most cases, this is easily possible.
There are two common installation locations for integrating a backwater valve into the sewer:
- In the inspection chamber: If there is a connection manhole (sewer manhole) on your property in front of the house, the valve can often be installed directly there.
- In the exposed basement pipe: Alternatively, the backwater valve can be integrated directly into the existing main drain line in the basement.
Important! Think holistically about backwater protection
A backwater valve is only part of the solution. For effective protection, your wastewater system must be considered as a whole. As part of our certified backwater protection DerKanal creates a customized overall concept for you that provides security against water entering from the sewer.
Why a backwater valve alone isn't enough
Many homeowners install a backwater valve and then feel a false sense of security. However, the backwater valve is just one link in the chain. Why? There are two main reasons:
- Leaky Pipes: When the sewer is full during heavy rain, enormous water pressure builds up. If your valve is closed, water backs up directly in front of it. If your pipes on the property have fine cracks or leaky joints, the water won't push through the drain, but instead through the damaged pipe directly into the ground, flooding your basement from the outside.
- The "Internal Backup": When the backwater valve is closed, not only does no water come in from outside – your own wastewater can't get out either! Anyone who showers or flushes the toilet at that moment will flood their basement with their own wastewater.
That's why technology alone isn't enough. True protection against water damage only works with a comprehensive system. This includes, among other things, leak tests of the pipes and intelligent drainage planning. Find out more here in detail about our holistic backwater protection and how we comprehensively protect your home.
5 Steps to Backflow Protection
Many homeowners shy away from installing a backflow valve because they fear a major construction site. But don't worry: with proper planning, retrofitting is usually quick and clean. Here's how the path to certified backflow protection looks at DerKanal from:
1. Free Initial Consultation
In an initial, no-obligation consultation, we clarify your basic situation: Have you already experienced backflow problems? Which areas of your house are below street level? We'll give you a preliminary assessment. For an initial self-assessment, we recommend taking a look at our Backflow Checklist.
2. On-Site Analysis
Our experts use state-of-the-art sewer camera technology to inspect your wastewater system, identifying the exact routing of your pipes and hidden weak points. This precise camera inspection is an essential basis for carefully planned and effective backflow protection. The costs for the Sewer Camera Inspection depend on the length, accessibility, diameter, and complexity of the lines to be inspected. To give you a non-binding initial estimate: an inspection of approximately 30 linear meters costs between €300 and €450.
3. Transparent Quote
Based on the results of the sewer camera inspection, we know which protective measures (such as mechanical/electrical backflow valves or pressure-tight cleanouts) are necessary for your property. Only with this clear picture can we then provide you with a customized and fair quote for the actual backflow protection.
4. Professional Installation
As soon as you commission us, we get started. Our trained technicians professionally install the backflow protection. After installation, we perform a functional test and explain what you should pay attention to in everyday use.
5. Maintenance & Service
For backflow protection to function in an emergency, regular maintenance (approx. once or twice a year) is required and often mandated by insurance. We are happy to take on this recurring inspection and cleaning for you.
Maintenance of the Backwater Valve
Like any technical and mechanical component, a backwater valve requires regular maintenance. Wastewater contains fats, hair, soap residue, and dirt. These accumulate over time on the seals and moving parts of the valve.
If the valve is not maintained, the deposits can harden. In the worst case, the valve will no longer seal properly during a heavy rainfall event. Furthermore, insurance companies often require proof of regular maintenance in the event of damage. If this is missing, you will be left to bear the costs.
Therefore, have your system regularly (ideally once or twice a year) by a specialist company inspected and cleaned. You can find out more about the causes of backwater and how to take proper precautions in our general article on the topic of Backwater and Sewer Maintenance.
Advantages and Disadvantages of the Backwater Valve
Advantages of the Backwater Valve
- Protection: A backwater valve protects against water ingress from the overloaded public sewer during heavy rainfall or flooding. (However, this requires that the backwater valve was planned and installed as part of a comprehensive backwater protection system.)
- Cost-efficient: Installing a backwater valve is many times cheaper than renovating a property plagued by water damage. Because apart from the financial burden, the construction effort and the accompanying circumstances of extensive water damage are also extremely unpleasant.
- Easy to retrofit: Retrofitting a backwater valve in the sewer is possible for most properties without extensive construction work. For new builds, backwater protection should ideally be planned and implemented from the outset.
- Insurance Coverage: Many insurance companies absolutely require the installation of a standard-compliant backwater prevention system to cover costs in the event of damage.
Disadvantages of the Backwater Valve
- Maintenance Requirements: Without regular care, the seals can gum up. Regular maintenance (1-2 times a year) is essential.
- Risk of Internal Backup: If the valve is closed during a storm, your own wastewater cannot drain either. Anyone who then showers or washes will flood their own property.
- Prone to Blockages: Coarse impurities and solids from the drain can interfere with the closing mechanism. The result: The system will no longer close during a backflow event.
- False Sense of Security: If a drainage point (e.g., a basement bathroom) is below the backflow level without a natural gradient, a backwater valve is not sufficient – a lifting station is required here. Cleaning openings that are not pressure-tightly sealed also pose a significant risk. Conclusion: Effective protection always requires a holistically planned backflow prevention concept.
DerKanal: Your Partner for Backflow Prevention & Backwater Valves
When it comes to protection against water from the sewer, you should not compromise. With our certified backflow prevention we are recognized as pioneers and offer you the best possible protection against flooding from sewer water.. We plan and install backwater valves as part of a comprehensive backflow prevention system for customers in Vienna, Lower Austria, and Burgenland – and upon request also in Styria, Carinthia, Salzburg, and Upper Austria.
Every building is unique. Therefore, feel free to request a free initial consultation with us at any time. We will clarify your questions and find the best solution for your property.
Frequently Asked Questions about Backwater Valves
What is a backwater valve and how does it work?
Simply put, a backwater valve works like a one-way street for your wastewater. In normal operation, the wastewater flowing out of the house pushes open the internal flaps and flows unimpeded into the public sewer. However, as soon as water backs up in the street sewer and tries to push back into your house, these flaps automatically close due to water pressure (or, in electric models, by a motor).
What is a mechanical backwater valve?
A mechanical backwater valve operates purely on physical principles and requires no electricity at all. When water from an overloaded sewer pushes back towards the house, this water pressure automatically closes the integrated flap valves (usually two in a series).
When is it used? Building regulations only permit its use for faeces-free wastewater (greywater). It is therefore the right choice if only showers, bathtubs, sinks, or washing machines are connected to the drainage line to be protected. Its advantage: it is less expensive to acquire and quite straightforward to maintain.
What is an electric backwater valve?
In the electric version (also known as a motor-driven backwater valve), technology takes control. An integrated sensor constantly monitors the pipe. If this sensor detects a backflow, a powerful electric motor automatically and forcefully closes the shut-off flap. At the same time, a visual and acoustic signal (alarm) in the house warns of the backflow event.
When is it used? It is mandatory for wastewater containing faeces (blackwater). Therefore, as soon as a toilet is connected to the pipe section that needs protection, an electric model must be installed. The motor's power is so strong that it can even cut through solids or toilet paper when closing.
Myth: "A backwater valve is entirely sufficient as the sole protection against sewer water."
Unfortunately not! This is a dangerous misconception that often costs homeowners a lot of money. A backwater valve is an excellent and important component, but it's no miracle cure when considered in isolation. Errors frequently occur during retrofitting, which have fatal consequences during heavy rainfall. For the system to truly protect in an emergency, two factors are crucial:
- A comprehensive concept is needed: If the valve is installed in the wrong place or if the pipes on the property are leaky, the water will find another way into the basement. That's why we at DerKanal always rely on a holistic system that also considers risks such as "self-ponding" or leaky cleanout covers.
- The maintenance requirement: A backwater valve is constantly submerged in wastewater – surrounded by dirt, grease, and hair. Without consistent maintenance, the mechanism will gum up and the component will fail precisely when it matters most.
Conclusion: Only the combination of professional planning (holistic backflow protection) and regular maintenance guarantees you a permanently dry basement and full insurance coverage in case of damage.
What costs should I expect for a backwater valve?
The exact costs for a backwater valve, including installation, cannot be reliably quoted as a flat rate, as the conditions vary for each property. The final price depends on two key factors:
- The model: A simple mechanical flap for greywater is significantly cheaper to purchase than a sensor-controlled, electric motor backwater valve for toilet wastewater.
- Installation effort: If the valve can be installed relatively easily into an exposed pipe in the basement, the costs are lower. However, if the floor needs to be broken open or excavation work is required for installation into an inspection shaft outside the house, the effort increases accordingly.
Our tip: As part of our certified backflow protection we offer you a free initial consultation. After a professional on-site analysis of your situation, you will receive a transparent offer from us, precisely tailored to your building's needs.
What is the difference between a backwater valve and a backflow flap?
While "Rückstauklappe" (backflow flap) is the more common everyday term, the technically correct and standardized term for the component is actually "Rückstauverschluss" (backwater valve). The difference lies in the details:
- The backwater valve refers to the complete, standard-compliant, and secure overall component (e.g., according to DIN EN 13564). This usually consists of several elements, such as two flaps arranged in series or a motorized system for wastewater containing faeces.
- The backflow flap (often in the form of a mechanical swing flap) is, strictly speaking, only a single, movable part within this backwater valve.
