Water demand garden/year --> Is a cistern worthwhile?

As already stated, it is not cost-effective but still sensible. The cistern should just be larger. Only then can you buffer sufficiently (e.g. heavy rain, etc.) The lawn requires about 20l/m2 per week. For 100m2, that is 8,000 liters per month. With a cistern, you should be able to bridge a dry period of 3-4 weeks. There have also been prohibitions on watering with fresh water. With a cistern, you are initially off the hook.

Lawn requires about 20 liters/m2 per week.
For 100m2 that means 8,000 liters per month. With a cistern you should be able to bridge a dry period of 3-4 weeks.
There have also been bans on watering with fresh water. With a cistern you’re initially in the clear.

I’m trying to reach at least 10,000L with additional tanks or barrels that might also be supplied by the cistern’s overflow. It’s just annoying if you can’t arrange something bigger from the ground up. At some point those things also start to get really expensive.

A cistern never pays off. But I think you have a better feeling using rainwater rather than drinking water in the garden.

I also have a small question about this: Could/may one use a shipping container as a cistern? Shipping containers are comparatively inexpensive and also watertight or can be sealed with minimal welding effort. Considering a volume of about 30 kL, it would basically be an interesting idea. But is this prohibited by building regulations or are there other reasons why it is not seen anywhere? Pools are sometimes already made from them.

With 1000 liters you won't get far. I could only bury a 4 m³ cistern, I would have preferred at least 6 m³.

If it is done by yourself, you can save a lot. I spent about €1500 on the cistern, drainage channels, new pipes, etc.

It was pointed out several times here that a cistern is not financially worthwhile.

I would not necessarily see it that way. Our cistern was built precisely to save money. Or rather, to no longer have to pay the rainwater fee. Thus, the investment has already paid off after a few years.

Tell me, do you all really need golf-course-quality grass in your gardens or do you have 4000 sqm plots?

I have 1600 sqm of land, of which at least 1000 sqm is undeveloped (the rest is residential building, driveway, double garage, shelter, garden shed).

I have several fruit trees, (still smaller) about 22 sqm of berry bushes, a raised bed, and nearly 100 sqm of vegetable growing area.

For that, I only need 1 IBC container with 1000 liters. So far, I’ve never run out of water in the last 2 years. I’ve also never had to use tap water (I only use it sometimes when there are just small things to water, because I’m too lazy to start the pump for just one watering can).

The lawn is not watered; you don’t need that. If you never do it, the roots grow deeper. Only in the summer of 2018 did it look less than optimal for a few weeks, but it recovered really well.
And the bed is mulched, so you don’t have to water much there either.

So I can’t really understand this 6-10 sqm cistern.

Back then, I even thought about getting a third IBC so I’d have 3 sqm. But as I said, I’ve done great with this for the last 2 years. You just shouldn’t spoil the plants too much; then their roots grow nicely deep.

And last year I couldn’t keep up with the vegetables from the garden, so even with little water it produces a lot. Over 200 kg of tomatoes and tons of zucchini, pumpkins, various cabbages, chard, lettuce, strawberries, etc.