Rainwater cistern: Useful? Necessary? Costs?

Hi,

in a contract for work we are offered:

Rainwater cistern and wastewater connection
Construction of a concrete cistern with approx. 5.4 m³, up to 5 m from the building including piping and backfilling with connection to the roof drainage. The wastewater pipe will be led from the base slab to the existing wastewater transfer shaft and connected.

What do you think?
- Are the cistern and wastewater connection directly related?
- Do we need the cistern? For what purpose? What if we don't have it?
- What cost share is probably associated with it (not shown separately, of course, I will also ask the provider)?

The cistern was mandatory for us. Other municipalities usually also charge a monthly fee. The water from your roofs has to go somewhere after all!

With us, it was not (yet) mandatory, but we were explicitly advised to build a cistern for garden irrigation. Our waterworks manager, on the other hand, is very reluctant about it as a domestic waterworks... It probably won't pay off here according to the current situation. However, it becomes interesting when dirty water and rainwater are collected separately, or when wastewater fees are calculated not only based on water consumption but also on the sealed surface area. Then a recalculation would be necessary...

Do you have a submersible pump in the cistern? Or how do you get the water out? (I only know it from my parental home, where there is a cellar, so that the cistern can be almost completely emptied directly via a tap.) How is your cistern accessible for inspections? Manhole cover? Where is the cistern located?

A cistern rarely pays off.

But I don't care whether the sprinkler runs for 5 minutes, 30 minutes, or 60 minutes ...

Do you have a submersible pump in the cistern?

No, it is an infiltration cistern. Water collects there automatically and is slowly released again. We ourselves do not benefit from it. It is located on the side, about 4 meters from a downpipe.