Rainwater cistern yes or no and which material?

Does a cistern ever make sense if it is not required?

From a certain water consumption, you can get exempted from wastewater costs for outdoor water here,

Oh, how nice that would be.

Then the m³ only costs 2,xx€ instead of 6-7€. The neighbors used about 20-30m³ last year.
Now you can compare the acquisition costs + interest costs against that.

Did they scrape off the dirt or are they possibly athletes who use "different" shower options.
I believe we have on average 7-8 m³ consumption per month - if I’m not mistaken. 2 adults + 2 small children, for whom the bathtub is usually only "half full."

where the bathtub is usually only "sitzvoll".

what is "sitzvoll" for children is determined by displacement in our case

From a certain water consumption, one can be exempted from wastewater costs for the external water with us. Then the m³ costs only 2.xx€ instead of 6-7€. The neighbors used about 20-30m³ last year.

It was only about the external water for garden irrigation. I don’t have any figures for last year because I only seeded the lawn in September.

It was only about the outdoor water for garden irrigation. I don't have any figures for last year because I only seeded the lawn in September.

Oh - I must have missed something there ops:.

.1) How large should the cistern be at least? 2.) What costs should I expect? 3.) Is the purchase worthwhile? 4.) How is the water extracted? 5.) Can the cistern be connected to the outdoor water tap?

(Numbering by me.) I am assuming a cistern that collects surface water/rainwater.

1.) It depends (area over which water is collected, i.e. roof projection, possibly garage, all surfaces draining into the cistern. Then the rainfall amount. You can find calculators for this on the internet, often at the manufacturers. Unfortunately, links are not allowed here). 2.) Costs? Get a quote (if you find the calculator, you will also find a supplier). 3.) That depends. After sizing the cistern, you have an idea of how many m³ of water you can estimate per year. The costs for that, if you take it from the drinking water network (separate outdoor meter or not) can be obtained from your utility company. Then you do an investment calculation for the cistern, with the result that it will pay off after X years — or not. 4.) Usually by means of a submersible pump or submersible pressure pump. Hand pump is also possible. 5.) Is that sensible? The cistern only needs a fresh water supply if you plan rainwater use inside the house. If it is only for garden irrigation, the cistern does not require an additional supply. You can additionally provide an outdoor water tap (possibly with a separate meter) alongside the cistern, but you do not have to.

Regarding 1: We have 6,000l. In the past two years it has run empty once. But we have a small garden. Regarding 5: We have an external water tap for the cistern. Practically a pipe from the cistern into the outer wall and a tap there. A little next to it is an additional external water tap that is supplied with fresh water.