ᐅ Is a Cistern Economical with a Pumping System?

The water from the well is often very alkaline or contains a lot of iron. Not all plants tolerate this well. Rainwater is perfect for plants. However, economically it is usually not worthwhile.

When it comes to irrigation, the question is always what your needs are. If you water your English lawn twice a week with 20 liters per square meter (0.7 gallons per square foot) each time, a standard rainwater tank won’t be sufficient. However, most people don’t need that much, and after three weeks of dry weather, watering 250 square meters (2,690 square feet) once will work fine with a 5 cubic meter (1,320 gallon) tank. There will even be some left over for the vegetable garden. Of course, adding a well on top of that is probably not cost-effective.

WilderSueden schrieb:

When it comes to irrigation, it always depends on what you want. Someone who waters their English-style lawn twice a week with 20 liters per square meter (0.45 gallons per square foot) each time won’t be happy with a standard rainwater harvesting tank. Most people don’t need that much, and after three weeks of drought, watering 250 square meters (2,690 square feet) once is possible even with a 5 cubic meter (660 gallon) tank. That even leaves some water for the vegetable garden. Of course, using this alongside a well is probably not cost-effective.

Not everyone has only 250 square meters (2,690 square feet). Waiting three weeks of drought to water once is not an option, as by then most plants will be dead or at least done for the season. It’s not just about lawns or vegetable gardens, but also perennials and hedges. And you don’t want to sit in a dry garden during summer; ideally, there should be some green space (it doesn’t have to be an English-style lawn) and plenty of flowering plants.

Three weeks of dryness doesn’t rule out green and colorful surroundings. There are plenty of plants, especially among perennials, that cope very well with dry conditions. Meadows and herb lawns handle drought quite well and recover very quickly after rain. Trees and shrubs can root deeply, which is enough to survive three weeks without rain. Even in the sandy soils of Brandenburg, there are plants in the wild that manage well with what nature provides and are attractive to look at. 😉

And don’t underestimate how much area will need watering in the end. Let’s take a house measuring 10 x 10 meters (33 x 33 feet) plus eaves strips, a garage, a garden shed, patio, driveway, paths… you quickly add up to around 300 m² (3,230 ft²), which is typical for many modern plots of land.

Here I have 270m² (2,900 sq ft) of lawn that stays green all year round, like from a picture book, along with hedges, many roses, and a vegetable bed. I like to water generously, yet I have never emptied the rainwater tank. I’m all for everyone having their own well, but the doomsday scenarios claiming that everything dies after just three weeks of summer weren’t something I experienced here. On the contrary, I watered heavily and after the next thunderstorm, the tank was full again. So please, let’s not spread scare stories.

And by the way: groundwater levels can also drop, and during dry periods, it can run out as well. So even if my rainwater tank ever does run dry, you still have to consider how deep a well is.

Rainwater is not only excellent for irrigation but can also be used, for example, to clean photovoltaic systems (of course, not in the sun) because it doesn’t leave lime scale spots.

I would like to point out that water from a cistern must be pumped out using a pressure pump, costing around 30-40 cents per kWh, while garden water flows naturally from the tap at 3-5 bar (45-75 psi). Such a pump costs about 200 to 300 euros, doesn’t last forever, requires filter replacements, and so on. Sprinkling the lawn for 2 to 3 hours can easily use up 1 kWh.

In other words, operating a cistern is not free.

A cistern only pays off after many years. In winter, it is always full, so additional drainage is needed, which again means extra costs.

And in summer... what are 5,000 liters (1,320 gallons) in the peak of summer? It will evaporate into the air before it even reaches the lawn.