self-sufficient house on farmland

So I have to say you all really surprise me very positively here already after one day I have found enough suggestions and ideas to keep myself busy for a few weeks! Thank you so far! only with the building permit it is such a thing because I just don't understand the jargon in the law books. Building in the outer area ... ok, but with most of the terms I can't do anything yet at the moment, I probably need more info first. Best regards

Why don't you just go to the [Gemeinde], to which the piece of land belongs, and ask if you are even allowed to?

Well,
for water treatment, some filters that treat water from the groundwater can be sufficient, but it is always better to regularly check the water.
Electricity can be generated via photovoltaics and a combined heat and power plant. Just google Ecoisland. Island systems store energy in accumulators.
Wastewater must now be biologically treated. However, there are cost-effective options for this. Since you are building new, you can also use good possibilities here, which are usually limited by the property.
However, there may be a connection obligation from the municipality. You should inform yourself about this.

If you want more suggestions: rainwater use for the washing machine and toilet to protect the groundwater.

Hello Christian,
as soon as the positive decision from the building authority regarding your [Bauvoranfrage] has arrived, you will get back in touch here. Until then, you can set aside all other questions and considerations.