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What is the Backflow Level?

The backflow level is the height to which wastewater in the sewer system can rise when overloaded and potentially push back into connected buildings. It is typically at the level of the street surface in front of the building. All drainage points below this level — floor drains, toilets, basement showers — must be protected against backflow.

By Jonas Derissen, Managing Director of Drainbee GmbH 2 min read Updated

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ways: valve or lifting station
2
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± 1 cm
probe measuring range
0–1 m
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How does it work?

During heavy rain or sewer blockages, the public sewer system can no longer handle the volume of water. Water backs up in the pipes — up to the backflow level. All drains below this level then become potential entry points for sewage from the sewer system.

The exact position of the backflow level is determined by the local municipality and defined in the drainage bylaws. In most cases, it corresponds to the top of the street surface at the building's sewer connection.

Rooms below the backflow level may only be drained via a lifting station or a backflow valve. A direct connection to the sewer is not permitted for these rooms, as it offers no protection against backflow.

The basic rule under DIN EN 12056-4 and DIN 1986-100 is the lifting station. A backflow valve is only permitted under conditions: the rooms are of minor use, a toilet above the backflow level is available, and the drains can go unused during backflow. And in flood zones the backflow level is not enough as a benchmark: there the water in the sewer can rise to flood level, i.e. above it.

What does this have to do with Drainbee?

Drainbee monitors the water level in drainage systems below the backflow level — exactly where the risk is greatest. When a backflow event is developing and the water level in the pump sump or lifting station rises, you are immediately informed.

This allows you to check whether your backflow protection is working and take quick action if needed — before sewage enters your basement.

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Frequently asked questions

Where can I find the backflow level of my building?
The backflow level is defined in your municipality's drainage bylaws. It typically corresponds to the street surface level. If in doubt, your local wastewater utility can provide information.
Which rooms are below the backflow level?
Typically all basement rooms with water connections: basement bathrooms, laundry rooms, hobby rooms with floor drains, and underground parking garages.
Do I need to protect rooms below the backflow level?
Yes, according to applicable standards and municipal bylaws, all drainage points below the backflow level must be protected against backflow. As a rule with a lifting station, with a backflow valve only under certain conditions. The municipality is not liable if you fail to do so.

Sources

  1. BMWSB: Hochwasserschutzfibel – Objektschutz und bauliche Vorsorge (2022) (opens in a new tab)
  2. SUN Stadtentwässerung und Umweltanalytik Nürnberg: Schutz vor Rückstau, Starkregen und Hochwasser (opens in a new tab)
  3. Stadtentwässerung Dresden: Hinweisblatt Rückstauschutz – So schützen Sie Ihr Eigentum (2019) (opens in a new tab)
  4. DIN Media: DIN 1986-100:2016-12 – Entwässerungsanlagen für Gebäude und Grundstücke – Teil 100 (opens in a new tab)

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