House too deep in the ground, groundwater entering through the basement window

Hello,
we built in 1991 and explicitly pointed out that there could be a danger from flooding here. Our architect therefore arranged a trial excavation to see where the groundwater was coming from. Excavation approx. 3m.
He then said he did not want to commit to anything, the height should be determined by an employee of the city.
We moved into the house in 1992. In 1993, groundwater then flowed into the basement.
My now deceased husband then called the building authority of the city and explained the situation. The gentleman who determined the height explained that he had based it on the height of the surrounding houses and that it had been a hundred-year flood, and that we could not assess this at all.
However, none of the neighbors had the problem, all about 80 cm higher and still 6 steps up to the front door.
My husband then, as a precaution, glued panes in front of the basement windows with an air slit for ventilation.
1994 again a hundred-year flood!!! The water was now about 20 cm high at the basement windows. Thank God secured by the precautionarily installed panes. My husband called the gentleman again, but heard nothing more. And the architect referred to the gentleman from the building authority. In 1994 we pumped water out of the basement shafts all night. My husband said at the time, this is an authority, we have no chance.

The house is simply too low,
now a new problem!!!! A flood retention basin is to be built here. The architect died immediately after our house was built, the gentleman who determined the height retired. The city says it was approved by the district office, yes, that’s correct, but a red stamp on the plan explicitly states that the city building authority must be consulted for the height determination.

If the retention basin is built, the groundwater is expected to rise by about 25 cm more, then I have no chance of pumping it out anymore.
Also, I wanted to sell the house, which due to this defect is not possible or only with a considerable reduction in value.

My question now, how much reduction in value should be assumed here?
Also, what permanent solution could be installed to protect against the ingress of groundwater. I would need a solution that provides relief as long as the house exists.

Thank you for your answers

My question now is, how much depreciation should be applied here?

I see no chance to answer you without it becoming individual legal advice. By the way, your settings prevent me from sending you a private message.

Can't you rephrase your answer as a non-binding opinion?

Hi,

without wanting to be rude, but what exactly do you want?

You built a house in a flood area/area with an extremely high groundwater level about 30 years ago (whether one or the other or both I cannot tell exactly from your post). Apparently without designing the construction accordingly. No idea if a waterproof concrete shell was already common back then, but flood-proof basement windows certainly existed. However, you apparently did not install them, for whatever reason.

Apparently you think the house was planned too deep? If that only becomes apparent after 30 years, it will be difficult to complain...

Best regards,
Andreas

Can't you rephrase your answer as a non-binding opinion?

In this case, I see no answer worth giving, the preparation of which the RBerG would not prefer to be done in the law firm rather than at the regulars' table without good reason.

I see in this case no answer feasible, the elaboration of which the RBerG does not prefer without reason in the law firm rather than at the regulars' table.

Simply adapt the spelling from the Jura forum, then it fits