Water Connection Garage - Drainage Planning Developer

Hello everyone,

this is my first post in the forum. I hope it is understandable enough.

We are building with a developer in NRW and purchasing a house with a garage and a plot of land.
We would like to have a water connection and a drain installed in the precast concrete garage in order to attach a washbasin there (red dot in the floor plan).
Unfortunately, we received a response stating that apparently only a water tap could be installed (similar to an outdoor tap located at the terrace). A drain could not be installed because the drainage plans have already been submitted to the building authority.

In our ignorant opinion, the outdoor water connection is not a problem because the water line runs under the garage to the outdoor tap.
For the drain, an additional pipe would have to be laid under the garage to the kitchen. Unfortunately, we do not know exactly where the water shaft is, but it will be located in front of the kitchen towards the sewer (see shaft in the kitchen).

Is this new drain a drainage plan change and if so, would it require approval at all?
Is this planning even feasible?

Thank you very much for comments and feedback.

Best regards
Neuling89 :)

To simplify the situation a bit, I have drawn the water pipes in a simplified manner. In the event of a drain in the garage, the rainwater would then become wastewater. Which, according to my understanding, should make no difference because it flows into a combined system anyway.

I hope that I have understood everything correctly. One question in advance: Are you absolutely sure that you have a mixed water system?

Regarding the faucet itself, there should be no problems. I assume that the water pipe comes out of the floor somewhere in the garage and from there is routed outside through the wall. A small branch can go to the sink here. I assume that the sink only needs cold water, right? You do have a pressure loss when you use the sink and, for example, a lawn sprinkler at the same time, but that should be negligible.

The drain is the bigger problem. Basically, every place where wastewater is discharged must be approved. Additionally, a leak test must be performed inside the building (with us, they even required a DVD of the camera inspection). A supplementary application to the building authority should not be a problem. It is sufficient if a small water pipe with a diameter of 5 cm is led through the garage floor to the wastewater pipe. The technical effort is also manageable.

I hope that I have understood everything correctly. One question in advance: Are you absolutely sure that you have a combined sewer system?

Regarding the faucet itself, there should be no problems. I assume that the water pipe comes out of the floor somewhere in the garage and from there is routed outside through the wall. A small branch to the sink can go here. I assume that the sink only needs cold water, right? You do experience a pressure loss when using the sink and, for example, a sprinkler at the same time, but that should be negligible.

The drain is the bigger problem. Basically, every point of wastewater discharge must be approved. In addition, a tightness test must be carried out up to the building interior (with us, you even had to submit a DVD of the camera inspection). A supplementary submission to the building authority should not be a problem. It is sufficient if a small water pipe with a diameter of 5 cm is routed through the garage floor to the wastewater pipe. The technical effort is also manageable.

Thank you for the feedback.

I am 100% sure that it is a combined sewer system. I have seen photos of the pipes under the street and in the drawings it is also described as a combined system.
We only need cold water for the sink, that is correct.

There is a DN 70 collector pipe in the garage (I assume HT). We would then connect the wastewater to this. (Unfortunately, I cannot edit the first post.)
The question that arises for us is whether we are allowed to simply discharge wastewater into the rainwater collector pipe if it is anyway carried on as combined wastewater to the sewer system (see floor plan-water attachment). I do not know whether a tightness test is necessary for the 80 cm pipe run.

So afterwards no one will check this anyway. Does the rainwater downpipe of the garage roof run inside the garage? In that case, I would simply connect a small branch afterwards. With some craftsmanship, you can do it yourself, and no one will really check it after the building inspection has been completed. Besides, you are not discharging any problematic wastewater through it. We also have a sink in the garage. I at most wash my hands thoroughly there after gardening or pour out some cleaning water if I have cleaned the windows outside.