Collect rainwater or drill a well?

Self-sufficiency is always good, but if you spend a lot of money on four weeks of self-sufficiency, and then actually need three months of self-sufficiency because it simply won't rain, that is ultimately quite uneconomical. Presumably, one could precisely calculate how much capacity a cistern at a certain location would need to have so that incoming rainwater and irrigation demand match as closely as possible...

That can be calculated quite easily. You just need to know the areas where you collect and the location. Then you have the max size that you can fill with rainwater. With an additional well, you can design significantly larger. Here you can collect continuously and also in winter. Here with us, you also pay for sealed surfaces. That is waived if you have a [cistern]... We have a 76m3 [cistern] and an old well. How long it lasts you also depends on the garden. 4 weeks are usually enough. We estimated about 6-8 weeks (including pumping from the well).

also goes bigger just didn’t want to rush ahead with “build cisterns <50m3“. With our manufacturer, the price difference between 76m3 and 92m3 was €3,000 net.

That is all far beyond the realistic reach of a normal single-family home builder. They have €50 water costs for garden irrigation per year. Five-figure amounts for cisterns are illusory.

50€ garden water??? No garden or no irrigation?
Anyone who needs so little doesn’t have to think about it.
In many areas, the decision whether to have a cistern or not is taken away from you. These are usually retention cisterns.
For those who have a few m2 of space and want to maintain it even during dry periods, they should consider it. We in the south do not have a water shortage. But it is very calcareous. Another point in favor of rainwater. Garden is a hobby...
Otherwise, you could just take a smaller plot or let it go wild.

€50 garden water??? No garden or no irrigation?
Anyone who needs so little doesn’t have to think about it.
In many areas, the decision whether to have a cistern or not is taken away. These are usually retention cisterns.
For those who have a few m2 of area and want to maintain it even in dry weather, they should think about it. We in the south have no water shortage. But it is very hard (high in lime). Another point for rainwater. Garden is a hobby...
Otherwise, you could just take a smaller plot or let it go wild.

A normal single-family house today stands on 400-800 sqm and an irrigation system is used in the per mille range. Our lawn is green despite hot summers and the plants are doing well. 30 cubic meters are enough here.