Rainwater cistern yes or no and which material?

I would have a well flushed and that costs us depending on the service provider and invoice request 150 - 500 EUR.

I would have a well flushed and that costs between 150 - 500 EUR here depending on the service provider and billing preference.

That is cheap. For nearly 10m drilling + pump and pressure switch, it was about 1,000€ here.

How is the water withdrawal done? Can the cistern be connected to the outdoor water tap?

The cistern water may be connected to a separate outdoor water tap, but not to the already existing tap that is supplied with drinking water...

Otherwise: municipalities nowadays like to specify the method of money burning by statute, and you can't even comfort yourself with a green thumb...
If the earthworker will dig the hole for little money, better to start on your own, have the cistern delivered and installed, and possibly build the supply and overflow yourself (or ask the earthworker again...)

the municipalities nowadays like to specify the money-burning method by statute

So no one is surely forced to get a cistern (counterproof?). In my opinion, one must distinguish between infiltration (infiltration shaft, soakaway, etc.) and cisterns for rainwater use. And in terms of use again between use for garden irrigation or use inside the house (washing machine, toilet flushing, ...). And only infiltration is often mandated.

By the way, I have now calculated a demand for us of 7 m³ to 25 m³ cistern volume (only garden irrigation). The range results from the assumption about irrigation demand (100, 150, or 250 L/m²/year). The sheer size comes from the large property (approx. 1200 m², which is not sealed), although most likely the irrigation demand does not increase linearly with the property size because one will somehow also practice less intensive gardening (I guess). A concrete cistern of 5.4 m³ costs us 1500 euros extra (somehow tangled up in the builder’s contract). That is roughly as economical as the concrete staircase or the controlled residential ventilation + heat recovery ... In my opinion, the 1500 euros must be put into relation with the green tanks that people otherwise subsequently buy at the hardware store (or not).

I know someone with a well that supplies very iron-rich water. Even washing the car is borderline. One always has to see on a case-by-case basis ... Rainwater is a quality of its own .

My father, I believe, has about 7,000 liters plus an above-ground tank for 1,500 liters. He often runs out completely in the summer - even though the property is only about 650 sqm (including the house and terrace). However, the garden is more of a utilitarian garden except for a maximum of 80 sqm of lawn. I don't know to what extent vegetables and flowers need more water than lawn.

So no one is forced to have a cistern (counterproof?). ).

yes, with us it is required in the development plan. Retention cistern with throttled outlet into retention basin.