What is Flooding?

• Surface water: heavy rain or a river flood stands against the building and runs in through window wells, basement windows, doors, garage ramps and basement stairs.
• Sewer backflow: the sewer is overloaded, and sewage pushes up through floor drains, showers and toilets in the basement. More under sewer backflow.
• Groundwater: after long rain or a flood, the groundwater rises and pushes through the slab, joints and pipe penetrations. It often arrives with a delay, days after the event.
• Failing equipment: the pump in the pump sump fails, the power goes out, a backflow valve sticks.

The distinction isn’t academic. It determines which protection works, and whether and how insurance pays.

Heavy rain can basically occur anywhere, the GDV stresses, even far from any river. According to the federal flood protection guide, sewers in built-up areas are mostly not designed for such events, largely for economic reasons. The water then finds its way over the surface.

Houses in dips, at the foot of slopes and on streets where water collects are especially at risk. The guide even mentions street names such as “Im Tal” (in the valley) or “Mühlenstraße” (mill street) as possible hints. Maps are more reliable: many German municipalities publish heavy-rain hazard maps, and the federal states publish flood hazard maps. And look at what has already happened at your place: where did water stand on the property after the last thunderstorm?

The BBK’s most important rule: don’t stay in the basement during a flood. According to the federal flood protection guide, even a few decimetres of water can be life-threatening if doors can no longer be opened or electricity is involved. Only enter flooded rooms when you are sure the power is off.

• Before: check and close backflow valves, switch off electrical appliances and heating in rooms at risk, pull the fuse if necessary
• During: stay in higher rooms, call 112 only in an emergency
• Only pump out once the water level outside is falling, otherwise there is a risk of uplift damage
• After: photograph and document the damage, notify your insurer, dry quickly, and have the structure, oil tank and electrics checked by professionals

According to the GDV, damage from heavy rain, flooding or sewer backflow is only covered by an additional natural hazards policy (Elementarschadenversicherung), not by standard German buildings insurance. Around 41% of residential buildings in Germany don’t have this cover. The federal flood protection guide adds two important points: for sewer backflow, insurers only pay if a fixed protective device such as a backflow valve or lifting station has failed. And damage from groundwater seeping in is generally not insurable, unless flooding pushes it to the surface and it runs into the house from there.

Tenants should also check whether their contents insurance includes natural hazards.

No sensor helps against water running in down the basement stairs. Drainbee also doesn’t detect water on the floor. The probe measures the level in a pump sump or lifting station, i.e. where a basement depends permanently on a pump.

That is exactly where many basement floods start without any flood outside: the pump fails, the float sticks, the power goes out. Drainbee alerts you when the level rises above your threshold, when the power fails and when the WLAN drops, by push or call-style alarm in the app. That buys time before the shaft overflows. With a flood coming from outside, it doesn’t replace any of the measures above.