Separation of Gas & Water - Who Pays in Old Properties?

oh man ^^

of course the piping is also part of the duties of the property owner.

if there is nothing in the purchase contract about "the old owner takes care of the dismantling of the old pipes," removing the house connections is definitely your problem and your expense.

somehow it's amusing that you so naively thought that you have no contractual relationship and that they should remove their mess from your property (heh heh). well then, have fun building..

You have bought a house. It is connected, meaning the house is linked to the utilities.

We will convert the electricity meter to construction power. But due to an air-water heat pump, we have no interest in gas, and the water pipe has to be newly installed anyway.

Is there a general regulation regarding this?

The contracts with the utilities do not transfer to the buyer. You have to take care of that yourselves.

I only fear that we are "automatically" customers because of the land purchase, or is that not correct?

You are confusing the connections with the providers.
You are responsible for dismantling.
For understanding: you buy a house and can basically move in immediately (condition doesn’t matter here, it is a house, whether it is habitable in your opinion or not). The meters are read, differences settled or paid by the seller. You take care of your own electricity and gas provider.
If you plan a renovation (or even demolition) where you do not need gas, that is your own interest. You can do whatever you want, i.e., cancel gas, dismantle, and then install another heating system.
The seller has done their duty: sold you a habitable property. If you want to change something, that’s your problem. The seller does not have to accept the toilet bowl if you decide to install a different toilet.
As seen, so bought.

Gas separation and dismantling will be handled by the municipal utilities. :-) The email arrived last week.