House behind the dam - what should be considered?

@Musketier: No, the other way around. Keller causes buoyancy due to water displacement.

@Musketier: No, the other way around. The basement provides buoyancy due to water displacement.

And a waterproof tub for the ground floor, not?

Basement is deeper than a [EG]

That is clear.
That’s why the topic of the basement was already settled.

But with a house with a ground floor tub, the same thing will happen during flooding. Overall, the water level naturally has to be higher for this.
But while with a basement the buoyancy might occur at about 2.50 m between the bottom edge of the tub and the water level, with a house on a slab it might happen already at 1.50 m between the bottom edge of the tub and the water level. (Height indications are freely estimated)
This is comparable to the draft of a light and a heavy ship.
With a house with a basement, in a single-family house usually the weight of at least 1.5 floors rests on the tub, while with a house on a slab only 0.5 floors. Additionally, the friction forces between the basement wall and the ground come into play.

I have to agree with Musketier... You can forget about the basement, I had the same problem when building my house... but regarding the actual topic of insurance, there are options during the construction phase. A BLV covers liability for unnaturally high groundwater and flooding, afterwards it only gets complicated or expensive because flood protection must be included in the building insurance, and unfortunately I don’t know exactly the situation of the property’s location. Before building, it’s best to talk to an expert to find out which factors need to be met, distance to the dike, etc. Of course, that always depends on the region and location.