ᐅ Annual Garden Water Demand – Is a Rainwater Harvesting System Worth It?
Created on: 18 May 2020 13:41
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Brainstorming
Hello everyone,
I am currently trying to estimate whether installing a rainwater cistern is worthwhile for our new build. We will have about 100 sqm (1,076 sq ft) of garden/lawn to plant. According to various online cistern calculators, I need roughly 8,000 to 11,000 liters (2,113 to 2,906 gallons) of water per year for this area in our region, which receives about 550 mm/sqm (22 inches/sq ft) of rainfall. The price for water and wastewater is approximately 2 euros per cubic meter. Based on this calculation, the cost for garden irrigation without a cistern would be around 22 euros per year.
If I now install a cistern with a capacity of 1,000 liters (264 gallons), I expect costs for the cistern, pump, and roof drainage connection to be between 1,000 and 1,500 euros. Assuming a budget of 1,000 euros, it would theoretically take more than 45 years for the cistern to pay for itself (without considering rising prices or repairs).
Am I missing something here? Could you possibly share your garden water consumption? Maybe the online calculators don’t match real-life usage.
Thanks
I am currently trying to estimate whether installing a rainwater cistern is worthwhile for our new build. We will have about 100 sqm (1,076 sq ft) of garden/lawn to plant. According to various online cistern calculators, I need roughly 8,000 to 11,000 liters (2,113 to 2,906 gallons) of water per year for this area in our region, which receives about 550 mm/sqm (22 inches/sq ft) of rainfall. The price for water and wastewater is approximately 2 euros per cubic meter. Based on this calculation, the cost for garden irrigation without a cistern would be around 22 euros per year.
If I now install a cistern with a capacity of 1,000 liters (264 gallons), I expect costs for the cistern, pump, and roof drainage connection to be between 1,000 and 1,500 euros. Assuming a budget of 1,000 euros, it would theoretically take more than 45 years for the cistern to pay for itself (without considering rising prices or repairs).
Am I missing something here? Could you possibly share your garden water consumption? Maybe the online calculators don’t match real-life usage.
Thanks
P
pagoni202013 Jun 2020 21:14Specki schrieb:
Tell me, do you all really need a golf-course-like lawn in your garden, or do you have 4000 sqm (about 1 acre) plots?
I have 1600 sqm (about 0.4 acres) of land, of which at least 1000 sqm (about 0.25 acres) is undeveloped (the rest is the residential building, driveway, double garage, shelter, garden shed).
I have several fruit trees, about 22 sqm (240 square feet) of berry bushes (still small), a raised bed, and nearly 100 sqm (about 1075 square feet) for vegetable growing.
For that I only need one IBC container with 1000 liters (about 265 gallons). So far, I’ve never run out of water in the last two years. I’ve also never had to use tap water (I only use it occasionally when watering very small areas, because I’m too lazy to start the pump for just one watering can).
The lawn is not watered; you don’t need that. If you never water it, the roots grow deeper. Only in the summer of 2018 did it look less than ideal for a few weeks, but it recovered really well. And the beds are mulched, so you don’t have to water much there either.
So I can’t really understand those 6-10 sqm (65-108 square feet) cisterns.
At one point I even considered getting a third IBC container to reach 3 cubic meters (about 106 cubic feet). But as I said, I’ve been fine with just one for the last two years. You just shouldn’t pamper the plants too much; then they root deeply.
And last year, I couldn’t keep up with harvesting all the vegetables from the garden, so even with little water, it produces a lot: over 200 kg (440 lbs) of tomatoes and lots of zucchini, pumpkins, different cabbages, Swiss chard, lettuce, strawberries, etc. I agree with this opinion. I used to have 900 sqm (about 0.22 acres) and planted everything with lawn, trees, flowers, etc. I watered whenever I thought it was necessary. I lived there for 30 years, and all the plants grew well despite my irregular watering.
When we built our new house, we poured a rectangular basin under the concrete basement stairs leading to the garden, sealed inside with waterproof slurry, and that was it. Roof water flows in, overflow on the other side. Nowadays, there are affordable plastic or prefabricated concrete versions. Its size was about 5 cubic meters (about 177 cubic feet), and the cistern was never empty.
We operated it with a standard household water pump. You have to be careful and somehow “pack” it to protect it from freezing in winter or simply drain it to avoid damage. We are building again now, and a cistern will definitely be installed again, 4-6 cubic meters (141-212 cubic feet), like the ones you can buy.
But in the end, as always, it depends on how you use it…
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pagoni202013 Jun 2020 21:21Anmacatili schrieb:
Just to get an idea. If I buy a cistern with, for example, 6000 liters (about 1600 gallons) capacity, which should be enough for our property, and a submersible pump, is it then possible with little effort to connect this to the outdoor water tap of the new house?
My parents have it this way but combined with a pressure pump system (for flushing toilets, etc., which I do not want). I would like to draw rainwater directly from the outdoor tap where I can also connect a garden hose...
What I don’t want is the cistern lid to be visible in the middle of my probably small lawn. I would rather place the cistern somewhere less noticeable.
Thanks to you all If you want to keep it simple, then bury the cistern somewhere accessible by the downspout. Pressure pump system plus suction pipe (available at hardware stores or online), and you can connect whatever you want to the pressure system. For example, we lightly buried an old garden hose or laid it along the edge to where we wanted it. We put a wooden post with a tap or an adapter for the hose there. I wouldn’t make a big deal out of it—just keep it simple. In the garden, you can usually lay everything out of sight, and if something goes wrong, the water just goes into the garden.
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pagoni202013 Jun 2020 21:25rick2018 schrieb:
And how do you refill the cistern if it ever runs dry?
For some uses, you’d prefer to use fresh water instead of cistern water. Not planning an external refill point is a false economy. For this rather rare situation, which will probably never happen with a 5m³ (176ft³) cistern, he simply connects his hose to the regular outdoor potable water tap or just uses the good old watering can on that day. But I don’t think it will ever be necessary.
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Anmacatili14 Jun 2020 12:37Thanks @pagoni2020. That’s how I will approach the topic as well. However, I actually have to include the cistern in the building permit / planning application, as I have just seen in the planning protocol. I would then plan it in a convenient location, have the downspout connections arranged accordingly, and set the location of the outdoor tap myself somewhere on the property, using a "wooden post and tap" or something similar.
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