ᐅ Is a Cistern Economical with a Pumping System?

WilderSueden schrieb:

Three weeks of drought doesn’t rule out greenery and color. There are plenty of plants, especially among perennials, that handle dry conditions very well. Meadows and herb lawns cope quite well with drought and recover extremely quickly after rain. Trees and shrubs can root deeply, so three weeks without rain is manageable. Even in the sandy soil of Brandenburg, there are plants in the wild that thrive with what nature provides and are visually appealing. 😉

And don’t underestimate how much area ends up needing watering. Let’s consider a house measuring 10x10m (33x33 ft) plus eaves strips, garage, garden shed, terrace, driveway, paths... you quickly reach around 300sqm (3,230 sq ft), which is typical for many modern plots.

I’d be happy to send you a photo next year showing how “beautiful” the plants look in nature after three weeks of drought. There’s no green left—everything is gray and brown. Of course, they recover after rain, but that’s not the kind of garden you’d want to live in.

And consider plots beyond new housing developments. There you might only have about 250sqm (2,690 sq ft) to water. But I don’t think that represents the majority of single-family homes in Germany. For example, my plot is 1,200sqm (12,917 sq ft), and that’s considered a small lot here in the village.

Tolentino schrieb:

The water from the well is often very alkaline or high in iron. Not all plants do well with that. Rainwater is perfect for plants. But yes, economically it usually doesn’t make sense.

Thanks, that makes sense – I wasn’t aware of that.

Let’s see what a cistern costs; as you say, it probably won’t be cost-effective...
But if the excavator is going to be there anyway, maybe it makes sense to do it at the same time.

motorradsilke schrieb:

And let’s move away from new building plots. There you probably only have to water about 250 sq m (2700 sq ft). But I don’t think that represents the majority of single-family homes in Germany. For example, I have 1200 sq m (13,000 sq ft). And that is considered a small plot in this village.

And you want to water those 1200 sq m (13,000 sq ft) twice a week with treated drinking water, in an area suffering from drought and water shortages. Excellent.

motorradsilke schrieb:

I’ll gladly send you a photo next year showing how “beautiful” the plants in nature look after three weeks of drought. There’s 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.

We can share those in the garden pictures thread. Mine should be presentable next year as well.

Whether it is cost-effective is just one of several factors – the often shortsighted focus on payback periods has contributed significantly to the climate crisis. In my opinion, the hidden costs of our consumption should be factored into the price of goods, including water.

Only a rainwater cistern can buffer heavy rainfall. Whether in the Oderbruch or the Ahr Valley, once the flood wave arrives, it is already too late. Therefore, I believe that a cistern should be mandatory in every new building today. The additional effort is minimal, while the benefits are substantial.

A basic course on proper garden watering would certainly be helpful for much of the population. The way water is currently wasted without reason or understanding is absurd.

If you only have a hammer, every problem looks like a nail.

A 250m² (2,690 sq ft) garden to irrigate is quite small, even for a new build plot, isn’t it? My plot is 612m² (6,585 sq ft), with the house taking up just under 100m² (1,076 sq ft). The terrace is planned at 30m² (323 sq ft), parking space for 2 cars about 40m² (430 sq ft), a shed 10m² (108 sq ft), plus paths, etc.

That leaves just under 400m² (4,305 sq ft), which according to the zoning plan I have to landscape with vegetation.

And with our stables of just over 600m² (6,460 sq ft), we actually represent the smallest possible plot category here.

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

Garden water costs me 2.15 EUR/m³ (about 8.14 USD/1000 gallons), plus a basic fee, plus additional costs for the meter, etc., so maybe 2.50 EUR/m³ (about 9.47 USD/1000 gallons).

This means my 7m³ (about 1,850 gallons) cistern filled to the brim has a “value” of 17.50 EUR (about 21 USD). From that, we must subtract extraction and maintenance costs, say about 15 EUR (about 16.50 USD) per filling?

Let’s take 100m³ (about 26,400 gallons) of garden water now, which everyone can scale according to their own needs. 100m³ equals 14 full cisterns, assuming I irrigate exclusively from the cistern (which is not really true). I then save about 210 EUR (about 224 USD) per year.

The concrete tank, including connections, cost me about 6,000 EUR (about 6,400 USD)... yeah, they really charged high prices here because they knew it was mandatory, I had no choice...

6,000 / 210 means I save money for the first time after 29 years. Then I can buy myself a bottle of wine. Hooray.

And anyone who believes that their small cistern buffers heavy rain...

Heavy rain, meaning what you see in the news as a disaster, is around 100 liters per m² (about 2 inches). That means on a typical roof area of 150m² (house, plus garage, plus conservatory, plus shed) about 15,000 liters (about 4,000 gallons) in a short time. Even if the 5m³ (about 1,320 gallons) cistern is empty at the start, it overflows after one third of the heavy rain event... which is pointless.

With heavy rain, the only solution is not to build where it actually occurs.

So we can agree that a cistern is not economically viable nowadays. However, it can help the garden (provided it’s not just an English lawn) to withstand short to medium dry periods. Rainwater is much better tolerated by some plants than tap water or even well water. In the future, water will become more expensive, and the use of drinking water will be increasingly restricted (some municipalities already have watering bans in summer from 7 a.m. to 7 p.m. or so). This often also applies to private wells to protect groundwater levels. Where it is already mandatory, there is no need for discussion.