ᐅ Are backwater valves always necessary in flood-prone areas?

Since we are currently planning the plumbing, I brought up the topic of backflow preventers. We have three points in the basement where wastewater is discharged outside. For some reason, they didn’t channel everything to one location...

The plumber says that backflow preventers are not planned for our system. Apparently, they are only required if rainwater is also discharged into the sewer system. In our case, this is not allowed, meaning only wastewater goes into the sewer.

Since we are building in a flood-prone area, I believe it is still possible that water could back up through the sewer system.

What do you think? Wouldn’t I need backflow preventers after all?

Ask your local authority about the maximum backwater level in the sewage system. If your building is at or below this level, or close to it, install a backwater valve. I would feel much more at ease with that precaution.

As far as I know, the height of the backwater level is simply determined by the height of the manhole covers, regardless of whether rainwater is drained there or not. The water cannot rise any higher because it would then flow over the cover onto the street.

If openings (toilets, drains, etc.) are below this level, these connections should be protected by a backwater valve. If drains carrying wastewater are below, I believe an electric backwater valve must even be installed. If the closure of the valve affects all toilets in a residential unit, a pump system must be installed that pumps the wastewater into the sewer despite the backwater.

Hello

All drainage lines below the backwater level, usually at the drain cover, must be connected to a lifting station for wastewater removal.
A backwater valve alone is not sufficient or professionally appropriate.

Olli

So, in the basement we only have the washing machine and a utility sink. There is also a small lifting station that pumps the water away. The site manager also says that we do not need backflow preventers...

Here is what the basement looks like: