ᐅ Cistern Dimensions – Building Plan Tips

Musketier schrieb:
Just to illustrate, we had a similarly sized garden last year (very dry) and needed about 30m³ (1,060 cubic feet) of water. With water and sewage costs of around €6 (if you cannot be exempted from sewage charges), that results in monthly costs of €15.
If you have to finance the cistern at about 1.5%, the system only pays off after roughly 29 years. (Assuming the cistern never runs dry during those 29 years.) Considering electricity costs for the pump, possible repairs, etc., the payback period would likely be closer to 35-40 years.

For those who don’t absolutely need to build a cistern, it probably never makes financial sense.

Each person has to run the numbers for themselves, as every water association (AZV) charges different rates for discharged rainwater. The trend seems to be increasing fees.
Therefore, I would definitely factor in an escalation rate for the fees when calculating payback...

If someone discharges rainwater and pays the associated fee, but also pays again for the garden irrigation sewage, the situation can quickly look different.

Additionally, some water associations (AZV) charge a rainwater fee even if the cistern is connected to the sewer via an overflow.

bierkuh83 schrieb:


Additionally, it should be noted that some water authorities also charge a stormwater fee if the cistern is connected to the sewer system (overflow).

Same here.
I was once told that due to the overflow, the cistern is not taken into account at all. This probably means that no flat-rate deduction is applied (e.g., if there is a cistern, they deduct 20% of the stormwater volume).

bierkuh83 schrieb:

Everyone has to do the calculation themselves, as each water authority has different reduction rates for discharged stormwater. The trend here is generally increasing (reductions).
So I would definitely include a capitalization factor for the fees in the return-on-investment calculation...

I always wonder how this is calculated.
The built-up area is clear. Building plans or inquiry with the builder.
But where do the water authorities get the stormwater volume from? Weather services – precisely allocated to the location? Internet? General assumptions?

No idea, there are definitely no regulations on that. The fee schedule from my water association only states the €/m² (euro per square meter) of sealed surface area. How they calculate that is probably only known to the accountant. You could probably look up the average nitrogen load per year and square meter and compare it to the sewage fee. But there are surely other factors involved (investments, capacity utilization of the sewer system, and incentives for infiltration, etc.)...

Hmm, this is a trickier topic than I initially thought. Very interesting to read.
I hadn’t considered the overflow issue either. So, having a smaller cistern with a well doesn’t really make sense because as soon as the cistern is full, I’ll have a problem... I definitely need to discuss this in detail again with the general contractor. But honestly, our development plan is really quite restrictive...

We are also charged based on the sealed surface area per square meter.

Fortunately, my surface water flows into a small surface water channel that leads into a stream. It only cost me a few meters of PVC pipe and saves me about 120 euros in fees annually.

Well, increasingly more zoning plans include this requirement. In our case, a rainwater cistern was mandatory.
Do you have a separate wastewater system? Then the overflow from the cistern can simply be connected to the stormwater drain. Otherwise, it needs to be able to infiltrate into the ground when the cistern is full.
A cistern probably won’t pay for itself quickly, or maybe not at all, but I still water my plants with it feeling better about it and more extensively than if I used tap water.
For me, using tap water to irrigate the lawn would be a bit too much.
An eco-friendly conscience for the price of a cistern.