Rainwater cistern: Useful? Necessary? Costs?

google "buy cistern online." You will find plenty of online shops that offer cisterns with all kinds of accessories (pumps, filters, lids, pipes, etc.). This will give you an idea of what to expect. In addition, there will be costs for the excavation and the subsequent backfilling as well as for the piping.

Hello,
we have a 6sqm concrete cistern. The cistern itself cost us around 900€ to install. It supplies our garden water taps. We also have a fresh water supply via the garden water meter. In addition, there are the house water system, pipes, excavation, etc. I estimate about 500€.
We only did this because the municipality pays an additional 160€ per sqm. So it didn't cost us much and we save the amount for roof drainage (which you have to pay here and is gradually increasing).
We buried the unit in the garden with a lid, which is covered with about 10cm of soil and then grass grows over it. You can't see it anymore. It would also be drivable.

Hi,
in a construction contract we are offered:
What do you think?
- Are the cistern and the wastewater connection directly related?
- Do we need the cistern? For what? What if we don't have it?
- What cost share probably applies to it (not listed separately, of course, I will also ask the provider)?

For us, the cistern was mandatory. Other municipalities otherwise charge a monthly fee. The water from your roofs has to go somewhere!

To my knowledge, there is no direct connection between the cistern and the wastewater pipe. Only the overflow of the cistern could be connected to the wastewater pipe (due to the height difference between the overflow and the wastewater pipe, contamination of the cistern water by possible backflow of wastewater should be prevented). (Layman's knowledge )
The most important point for you ( already wrote it): You have to find out what your municipality (federal state) requires. For us, one option for infiltration was specified by installing a soakaway, basin, pond, or cistern (I might have forgotten something). Since pond and basin on the property with small children (drowning risk) were out of the question for us (also, then the mosquitoes might lovingly greet you), and the installation of a soakaway would have cost quite some money, we decided on a 10 m³ cistern (concrete) for garden irrigation. I cannot give you the exact price (it was included as part of the complete construction contract), but the general contractor told us that the price difference between 5 and 10 m³ is "only" a few hundred euros.
My father has been irrigating his garden via cistern for years. He has (I think) 7.5 m³, which in summer sometimes gets completely emptied more than once. The entire property there is about 650 m² (including the house). Therefore, I think it pays off over a longer period to do irrigation via cistern instead of drinking water (especially since the wastewater fee is also based on drinking water consumption).
By the way: A cistern with overflow function into the sewer is not recognized here for lowering the "rainwater discharge fee" (information from the office). For this, all the water on the property must infiltrate. However, whether this works when large amounts of water occur and the cistern is already full, in my opinion, strongly depends on the respective soil conditions.

A cistern with an overflow function into the sewer system is not recognized by us for reducing the "rainwater discharge fee" (information from the office).

Logically, a cistern initially has no infiltration function (otherwise it would be an infiltration shaft, not a cistern).

The hints here help me anyway, now I can ask the right questions! If I learn more, there will be an update.

Logically, a cistern initially has no infiltration function (then it would be an infiltration shaft, not a cistern).

The hints here definitely help me, I can now ask the right questions! If I know more, there will be an update

As far as I know, the cistern can also be embedded in a larger gravel bed and the overflow used for infiltration. In that case, theoretically no discharge into the sewer system would be necessary. Thus, you would have a cistern with infiltration function and could possibly save the stormwater discharge fee. However, I consider this problematic because with a cistern already full and heavy rainfall, the soil might not be as absorptive as needed. This could then lead to the cistern being uplifted (even though it is made of concrete and filled with, for example, 10 m³).

However, I consider this problematic because with an already full cistern and heavy rainfall, the ground may not be as absorbent as necessary.

This requires proactive water management (and appropriate level measurement), then it will work. Anyway, one will have to prove an adequate infiltration concept, with or without a cistern. Infiltration on the property is one thing, cistern another (even if both can be presented together).