Surface Water Drainage and Backflow Protection

Hazard picture

Public sewers are sized for a statistically recurring, limited rainfall event; during heavy rain or network overload, sewage can be pushed back towards a building. Drainage points below the governing backflow level, such as those in basements, are particularly exposed, as are surfaces with inadequate surface drainage where rainwater pools in front of entrances and light wells.

Protection measures

All drainage points below the backflow level should in principle be drained via a sewage lifting station; backflow valves can only serve as an alternative where the served area is of minor use and a gradient to the sewer exists. A plot’s surface drainage – gradients, channels, infiltration areas – must be designed to discharge water without damage even in heavy rain, and critical entrances are additionally protected with raised thresholds.

Insurance relevance

Backflow damage is a frequently underestimated form of water damage, as it can occur regardless of a building’s distance from a watercourse. Many property policy wordings explicitly exclude backflow losses where no functioning backflow protection is installed, making evidence of code-compliant protection relevant to the scope of cover.