Infiltration system part of a turnkey house?

We purchased a turnkey house that includes all ancillary construction services - except those provided by public utilities. However, the construction company is now refusing to cover the costs for the infiltration system that we had to build on the property, as rainwater must be drained on the property and not discharged into the sewer system. In our opinion, a functional house also includes an infiltration system. It is not explicitly stated in the contract but is, for example, included in the drawing. How should we deal with this or does anyone have a similar problem?

I only know it this way: what is not in the contract is also not part of it. Depicting the system on drawings is not the proper way. However, I think you are powerless here.

What kind of costs are we talking about for such a system?

The house is turnkey after all. Drainage is not included, especially if nothing is stated in the contract. Usually, the construction work ends with the downpipe. The rest must be done by oneself or contracted separately.

It is certainly included in the drawing, since the "disposal method" of the rainwater belongs in the building application. Especially if, according to the development plan, it must infiltrate.

I think you will not get around paying the money separately here.

Your construction company already states that the local utility providers are not included. This includes: - Telephone / Internet - Electricity - Gas - Water - and of course sewage Sorry, you will have to pay for these yourselves. Our construction plans also showed a cistern, supply and sewage, but we naturally paid for these trades ourselves, since something like this, except in some cases with certain builders, never belongs to the scope of services...