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
@AleXSR700 We have a sloped site and use terracing, so no extra excavation was necessary.
We have a spring that we can pump from additionally. Rainwater from all roofs (which are also green roofs) and terraces is directed into the cistern.
We wanted to have a sufficient buffer, and the plot is also quite large (2500 m2 (0.62 acres)). Originally, we planned to go with a 92 m3 (3,250 ft3) cistern, but that would have interfered with the landscaping.
@Anmacatili Using rainwater for the toilets was a topic for us at first. However, it doesn’t really pay off due to the additional piping, filters, and possible deposits... better to use it for the garden. You still need a water treatment unit/pump.
IBC containers can occasionally be found on sites like eBay. If you have space, you can keep them in a shed or enclosure.
The best solution is a cistern at the lowest point so you can drain all surfaces, collect the largest amount of water, and save on stormwater fees.
We have a spring that we can pump from additionally. Rainwater from all roofs (which are also green roofs) and terraces is directed into the cistern.
We wanted to have a sufficient buffer, and the plot is also quite large (2500 m2 (0.62 acres)). Originally, we planned to go with a 92 m3 (3,250 ft3) cistern, but that would have interfered with the landscaping.
@Anmacatili Using rainwater for the toilets was a topic for us at first. However, it doesn’t really pay off due to the additional piping, filters, and possible deposits... better to use it for the garden. You still need a water treatment unit/pump.
IBC containers can occasionally be found on sites like eBay. If you have space, you can keep them in a shed or enclosure.
The best solution is a cistern at the lowest point so you can drain all surfaces, collect the largest amount of water, and save on stormwater fees.
Winniefred20 May 2020 13:36Cisterns are generally a good idea. Considering climate change, they are definitely useful. Unfortunately, we don’t have one yet but plan to install one when we redo the driveway (we have an older house, so everything was already set up that way).
Currently, we have about 500m² (5,380 sq ft) of garden and only 1,700L (450 gallons) of water storage in rain barrels. We will soon increase this to 2,000L (530 gallons), but even that won’t be enough. It has been too dry here for years. I don’t water the lawn at all; it has to survive or die on its own. For example, in April, we only had 4 liters (1 gallon) of rain. Almost no plants can survive on that. Additionally, we have a separate water meter to avoid paying the high wastewater fees on irrigation water. I water very sparingly and selectively, but when all barrels are empty—which often happens—I have no choice. Since last spring, I have used about 23,000 liters (6,080 gallons) of water in the garden, some of which was also for the children’s paddling pool. From the barrels, I roughly estimate another 5,000 to 10,000 liters (1,300 to 2,600 gallons), but I really can’t be precise.
It is definitely better for the environment, and I believe it will pay off considering climate change. Heavy rain events at least refill the cistern, so you have something to water with when it doesn’t rain for four weeks straight and temperatures exceed 30° Celsius (86°F). You simply can’t guarantee this volume with rain barrels alone.
Currently, we have about 500m² (5,380 sq ft) of garden and only 1,700L (450 gallons) of water storage in rain barrels. We will soon increase this to 2,000L (530 gallons), but even that won’t be enough. It has been too dry here for years. I don’t water the lawn at all; it has to survive or die on its own. For example, in April, we only had 4 liters (1 gallon) of rain. Almost no plants can survive on that. Additionally, we have a separate water meter to avoid paying the high wastewater fees on irrigation water. I water very sparingly and selectively, but when all barrels are empty—which often happens—I have no choice. Since last spring, I have used about 23,000 liters (6,080 gallons) of water in the garden, some of which was also for the children’s paddling pool. From the barrels, I roughly estimate another 5,000 to 10,000 liters (1,300 to 2,600 gallons), but I really can’t be precise.
It is definitely better for the environment, and I believe it will pay off considering climate change. Heavy rain events at least refill the cistern, so you have something to water with when it doesn’t rain for four weeks straight and temperatures exceed 30° Celsius (86°F). You simply can’t guarantee this volume with rain barrels alone.
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Anmacatili20 May 2020 13:47Just to get an idea: I’m planning to buy a cistern with, for example, 6000 liters (about 1600 gallons), which should be enough for our property, along with a submersible pump. Would it then be possible, without much effort, to connect this to the outdoor water tap of the new house?
My parents have a similar setup, but combined with a pressure booster system (for flushing toilets, etc., which I don’t want). I would like to draw rainwater from the outdoor tap, to which I could also connect a garden hose...
What I don’t want is for the cistern lid to be visible right in the middle of my probably small lawn. So I would prefer to place the cistern somewhere less obvious.
Thanks to all of you.
My parents have a similar setup, but combined with a pressure booster system (for flushing toilets, etc., which I don’t want). I would like to draw rainwater from the outdoor tap, to which I could also connect a garden hose...
What I don’t want is for the cistern lid to be visible right in the middle of my probably small lawn. So I would prefer to place the cistern somewhere less obvious.
Thanks to all of you.
Outdoor faucets must be equipped with a backflow preventer.
This way, you do not need an additional backflow preventer for refilling the cistern.
It is best to bury the refill connection at the same time. This means you do not have to block any faucet, run a garden hose to the cistern, or open the lid.
With a submersible pump or a well pump (providing sufficient pressure), you can then supply your irrigation system or garden hose.
Lids are also available in green or with a recess so they can be covered with vegetation.
The location should be at the lowest point so that all roofs, paths, driveways, etc., can drain into it.
This way, you save on charges for stormwater runoff.
This way, you do not need an additional backflow preventer for refilling the cistern.
It is best to bury the refill connection at the same time. This means you do not have to block any faucet, run a garden hose to the cistern, or open the lid.
With a submersible pump or a well pump (providing sufficient pressure), you can then supply your irrigation system or garden hose.
Lids are also available in green or with a recess so they can be covered with vegetation.
The location should be at the lowest point so that all roofs, paths, driveways, etc., can drain into it.
This way, you save on charges for stormwater runoff.
Before building with system separators, I would consider a separate setup and simply connect the submersible pump during the growing season to a conveniently placed stainless steel outlet/water column. You only need power to the cistern and an empty conduit to the outlet.
A proper submersible pump with pressure and flow sensors will ensure the water flows from the tap as usual when you open it. Maintenance is then limited to occasionally cleaning the inlet filter and draining the hose before the frost season.
A proper submersible pump with pressure and flow sensors will ensure the water flows from the tap as usual when you open it. Maintenance is then limited to occasionally cleaning the inlet filter and draining the hose before the frost season.
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