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Backwater - what is it?

During heavy rain, the water level rises above the so-called backwater level. This term is usually used to mean street level. Rooms in the basement or cellar quickly become flooded. The result: Damage caused by ruined flooring, furniture or electric appliances, soaked household goods and a great deal of hassle and costs for those living in the house.

For economic reasons, public mixed and rainwater pipes cannot be dimensioned in such a way that they can deal with extremely heavy rain without any problems. For this reason, flooding of the sewage pipes and backwater in all connected pipes must be expected in heavy rain.

Other reasons for backwater can be:

  • Blockage, burst pipes or damage to the sewage system.
  • Pump failure, if the drainage system is connected to a pumping station.
  • High water levels in the recipient (stream or river).
  • Pipe blockage or diversion due to repair work.
  • Increased wastewater feed, for example when sewage systems arebeing rinsed, the fire brigade is in action or more pipes are connected to the sewage system than originally planned.


Draining systems such as floor drains, washing machines, sinks, showers (grey water) or toilets (black water), which are below the backwater level have to be protected effectively and permanently against backwater. Wastewater that flows through gravity fed pipes into the sewage system have to be protected by a backwater valve. If the public sewage pipe is higher than the drainage spot, the wastewater must be pumped upwards via a fully automatic lifting station.


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