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
The original poster is installing an outdoor faucet anyway, so a backflow preventer is required.
Somehow, the rainwater cistern needs to be filled as well. Of course, you could run a hose from inside the house and leave it for hours, but I don’t know anyone who would consider that. Therefore, the classic outdoor faucet and this or a branch line should be used for refilling.
Somehow, the rainwater cistern needs to be filled as well. Of course, you could run a hose from inside the house and leave it for hours, but I don’t know anyone who would consider that. Therefore, the classic outdoor faucet and this or a branch line should be used for refilling.
Ah, then I probably misunderstood.
I thought he already had a regular drinking water tap on the facade and wanted to draw rainwater from that same tap at the same time. The cistern would be filled exclusively with rainwater.
To avoid any additional installation work later, I suggested a closed rainwater circuit with a submersible pump and an extra outdoor rainwater tap. If the cistern is empty, then just use the drinking water tap for watering and wait for the next rainfall. That was my idea.
I thought he already had a regular drinking water tap on the facade and wanted to draw rainwater from that same tap at the same time. The cistern would be filled exclusively with rainwater.
To avoid any additional installation work later, I suggested a closed rainwater circuit with a submersible pump and an extra outdoor rainwater tap. If the cistern is empty, then just use the drinking water tap for watering and wait for the next rainfall. That was my idea.
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Anmacatili21 May 2020 07:13I am currently installing an outdoor faucet that is connected to the drinking water supply.
The idea from @dab_dab sounds very interesting to me, so I will look into it further. You would need a cistern, a pump, and an external valve / water column. The pump requires power from the house (through a conduit), and the hose leading to the outlet point also needs a conduit. Is that correct? That seems quite doable to me. Thanks for the suggestion.
The idea from @dab_dab sounds very interesting to me, so I will look into it further. You would need a cistern, a pump, and an external valve / water column. The pump requires power from the house (through a conduit), and the hose leading to the outlet point also needs a conduit. Is that correct? That seems quite doable to me. Thanks for the suggestion.
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Anmacatili21 May 2020 07:55I would keep the outdoor water tap at the house since it is already planned. If the cistern is empty, I could connect a hose there to draw fresh water. Or am I missing something? The cistern would, of course, need to be connected to the roof gutters with pipes so that it can fill completely.
@Anmacatili exactly. But you might want to consider installing a pipe from the tap to the cistern at the same time. It might cost you around 20€. You can either switch the connection at the tap or screw a dual outlet valve onto the tap. This way, you can easily fill the cistern. Later on, you will probably want automatic irrigation. It’s easier if you always draw water from the cistern. The water line from the tap to the cistern and from the cistern to your outlet does not require a conduit. Just use HDPE pipe.
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