Is a cistern economically viable through pumping?

3 weeks of drought does not exclude green and colorful. There are plenty of plants, especially among perennials, that cope excellently with drought. Meadows and herb lawns handle drought quite well and recover extremely quickly after rain. Trees and shrubs can root deeply, then even 3 weeks without rain is enough. Even in the Brandenburg sand, there are supposed to be plants in the wild that manage with what nature offers and are nice to look at ;)

And don’t underestimate how much area there is to water in the end. Let’s calculate a house of 10x10m plus eaves strip, garage, garden shed, terrace, driveway, paths,... you quickly have 300 sqm together and are in the right range for today’s usual plots.

I’ll gladly send you a photo next year of how "beautiful" plants in nature look after 3 weeks of drought. There is nothing green left, everything is gray and brown. Of course they come back after rain, but you wouldn’t want to live in a garden like that either.

And move away from new building plots. There you surely have only 250 sqm to water. But I don’t believe that is the majority of single-family houses in Germany. I have, for example, 1200 sqm. And that is considered a small plot here in the village.

The water from the well is often very alkaline or contains iron. Not all plants tolerate that well. Rainwater is perfect for plants. But yes, economically it is usually not worthwhile.

Thanks, that makes sense - I wasn't aware of that.

Let's see how much a cistern costs, as you write, it probably won't be economically viable... But if the excavator is coming anyway, maybe it can be done at the same time.

And just move away from the newly built plots. There you surely only have 250 sqm to water. But I don't believe that is the majority of single-family homes in Germany. For example, I have 1200 sqm. And that is a small plot here in the village.

And you want to water those 1200 sqm twice a week with treated drinking water, in an area that complains about drought and water shortage. Excellent

I’d be happy to send you a photo next year of how "beautiful" the plants look in nature after 3 weeks of drought. Nothing is green anymore, everything is gray and brown. Of course, they come back after rain, but you wouldn’t want to live in such a garden either.

We’d gladly do that in the garden pictures thread. Mine should be presentable next year as well.

Whether it is worthwhile is just one question among several – the often very short-sighted focus on payback has caused us a large part of the climate disaster. IMHO, the hidden costs of our consumption should be added to the price of goods, and this also applies to water. Only a cistern can buffer heavy rain. Whether in Oderbruch or Ahrtal, once the flood wave is there, it is too late. Therefore, IMHO, a cistern should be mandatory in absolutely every new building nowadays. The additional effort is marginal, the benefit very large. A basic course on "proper garden watering" would certainly also be helpful for large parts of the population. How water is wasted nowadays in some places without sense and reason is absurd.

Who only has a hammer sees every problem as a nail.
A garden of 250m² to be irrigated is pretty small even for a new building plot, isn’t it? My plot is 612m², the house takes up nearly 100 of those. The terrace is planned at 30m², parking spaces for 2 cars say 40m², shed 10m², paths, etc.
That leaves just under 400m², which according to the development plan I have to green.

And with our roughly 600m² large livestock barns, we are actually the smallest possible plot category here.

Then you pave everything with (ecologically almost worthless) English lawn and can’t keep up with watering in summer... because the lawn with its short legs constantly needs water...

Garden water costs me 2.15 EUR/m³, plus basic fee, plus additional costs for the meter, etc., so maybe 2.50 EUR/m³.
That means my 7m³ cistern is full with a "value" of 17.50 EUR. From that, we have to subtract the costs for extraction and maintenance, say a filling costs 15 EUR?
I'll just take 100m³ garden water now, everyone can scale that to their own needs.
100m³ is 14 full cisterns assuming I can only water using the cistern (which is of course not true). Then I save 210 EUR per year.
The concrete cistern including connection cost me a good 6,000 EUR... yeah, they charged proper prices here because they knew the thing is mandatory, I have no choice...

6000 / 210... that means in 29 years I save money for the first time. Then I’ll buy myself a bottle of wine. Hooray.

And whoever believes their small cistern buffers heavy rain...
Heavy rain, meaning what you see on TV as a catastrophe, means about 100l/m². That is 15,000l in a short time for a usual roof area of 150m² (house plus garage plus conservatory plus shed). Even if the 5m³ cistern is empty at the start, it overflows after just 1/3 of the heavy rain event... that is useless.
With heavy rain, the only solution is not to build where the heavy rain occurs.

So we agree that a cistern is not economically worthwhile today. But it can help the garden (as long as it is not just English lawn) to survive short to medium dry periods. Rainwater is much more digestible for some plants than drinking or even well water. In the future, water will become more expensive and the use (or misuse) of drinking water will be increasingly restricted (there are already municipalities with watering bans in summer from 7 a.m. to 7 p.m. or so). This often also affects one's own well to protect groundwater levels. Where it is already mandatory, there is no need to discuss.