ᐅ Water Connection for Garage – Drainage Planning by Developer

Hello everyone,

This is my first post in the forum. I hope it is clear enough.

We are building with a developer in North Rhine-Westphalia (NRW). We are purchasing a house with a garage and a plot of land.
We would like to have a water supply and a drain installed in the precast concrete garage to be able to attach a sink there (red dot on the floor plan).
Unfortunately, the response we received was that apparently only a water tap could be installed (similar to an outdoor faucet located at the terrace). A drain could not be installed because the drainage plan has already been submitted to the building authority.

From our limited knowledge, an outdoor water connection should not be a problem, as the water pipe runs under the garage to the outdoor faucet.
For the drain, an additional pipe would have to be laid under the garage to the kitchen. We do not know the exact location of the water inspection chamber, but it should be in front of the kitchen leading to the sewer connection (see chamber in the kitchen).

Is this new drain considered a change to the drainage plan, and if so, would it require approval (building permit / planning permission)?
Is this plan even feasible?

Thank you very much for your comments and feedback.

Best regards
Neuling89 🙂

To simplify the situation a bit, I have drawn the water pipes in a simplified way.
If there is a drain in the garage, rainwater would then become wastewater. As I understand it, this should not make a difference since it flows into a combined system anyway.

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

Regarding the faucet itself, there should be no issues. I assume the water pipe comes up from the floor somewhere in the garage and is routed through the wall to the outside. A small branch line could go from there to the sink. I assume the sink only needs cold water, right? Although you will experience some pressure loss if you use the sink and, for example, a sprinkler at the same time, it should be negligible.

The drain is the bigger issue. In principle, every point where wastewater is discharged must be approved. Additionally, a tightness test must be carried out up to the building (in our case, a video inspection on DVD had to be submitted). An amendment at the building authority / planning office should not be a problem. It is sufficient if a small water pipe with a 5 cm (2 inch) diameter is routed through the garage floor to the sewage pipe. The technical effort is manageable.

BBaumeister schrieb:

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

Regarding the faucet itself, there shouldn’t be any problems. I assume the water pipe comes up from the floor somewhere in the garage and then runs outward through the wall. A small branch pipe could go from there to the washbasin. I assume the washbasin only needs cold water, right? You will experience some pressure loss if you use the washbasin and, for example, a sprinkler at the same time, but that should be negligible.

The drainage is the bigger issue. Basically, every point where wastewater is discharged must be authorized. In addition, a tightness test must be performed inside the building (where I live, you even had to submit a DVD of the camera inspection). Submitting an amendment to the building authority should not be a problem. It is sufficient if a small wastewater pipe with a diameter of 5 cm (2 inches) is routed through the garage floor to the sewer pipe. The technical effort is manageable.

Thanks @BBaumeister for the feedback.

I am 100% sure that it is a combined sewer system. I saw photos of the pipes under the street, and the plans also describe it as a combined system.
We only need cold water for the washbasin, that is correct.

There is a DN 70 (approximately 70 mm (2.75 inches)) collection pipe in the garage (I assume it is a PVC pipe, e.g., HT). We would connect the wastewater to that. (Unfortunately, I cannot edit the first post.)
Our question is whether we are allowed to discharge wastewater into the rainwater collection pipe if it is routed as a combined system together with wastewater into the sewer (see floor plan–water attachment). I am not sure if a tightness test is needed for the 80 cm (31.5 inches) long pipe.

Nobody will check that afterwards anyway. Does the rainwater downpipe from the garage roof run inside the garage? If so, I would simply connect a small branch pipe afterwards. With some basic DIY skills, you can do this yourself, and after the building inspection is completed, hardly anyone will check it thoroughly. Besides, you are not discharging any problematic wastewater through it. We also have a sink in the garage. I usually only wash my hands thoroughly there after gardening or pour out some cleaning water when I have cleaned the outside of windows.