Half of the roof does not drain - rework not possible - options?

Hello everyone,

unfortunately, at the end of the house construction, an unpleasant issue was noticed. The right half of the roof does not drain as planned in the drainage plan via the cistern but directly into the sewage shaft which is about 2m in front of it. The general contractor was there, and the excavator driver reportedly said that at the time, they could not dig deeper due to the boundary/foundations of the neighbor. Apparently, the slope of the drainage was not sufficient to reach the cistern because of this.

Personally, this really bothers me now because we installed an expensive cistern, have a large roof, and could really use the rainwater in the garden. The construction manager is now explicitly checking the heights again – but I am not sure if it might still work.

-->My question is, however, what claims/what amount can we assert if this can no longer be remedied?
among others through

[*]Lost rainwater (I have installed an irrigation system)
[*]Higher drainage fees due to discharge directly into the sewer instead of via the cistern
[*]etc.

I still have a retention and have set a deadline for remediation. So far, all defects have been remedied by the general contractor without objection, and I continue to strive for a cooperative relationship with the general contractor even during the warranty phase.

Thank you very much

What could not be dug deeper? The cistern?

What could not be dug deeper? The cistern?

Yes. That was the initial statement. But it will not be possible to set it any deeper...

Yes, there is little to be done at first. Basically, water can be pumped back up quite easily with pumps, so I would spontaneously suggest burying a small plastic cistern with an automatic pump that then pumps the water into the large cistern. It is more expensive than doing it right and planning it properly from the start, but that is not your problem.

How long is the distance from the downpipe to the cistern? A cross-sectional sketch with height specifications and distances would be helpful. If the connection to the sewer already exists, the pipe to the cistern could simply be laid non-frost-proof and the connection to the sewer could be designed as a safety overflow.

Thank you for the answers. We will review it again together with the site manager.

My question, however, goes in the direction of when it is no longer technically feasible.

What amount could I claim there? For example, the changed water fees over 30 years? The lost rainwater per year on average, etc.