Rainwater harvesting in Spain and price

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Rainwater harvesting in Spain and price

All you need to know about rainwater harvesting in Spain and price.

What’s the best Rainwater harvesting strategy in a positive house in Spain?

How does Rainwater harvesting in Spain work?

What’s the price of Rainwater harvesting in Spain?

May you don’t know us yet, let’s have a quick introduction: we’re ERA architects.
Actually, I’m Esther Rovira, architect and passive house designer in Barcelona, Catalonia and Andorra for either passive houses, efficient houses and positive houses.
In this post ‘Rainwater harvesting in Spain and price’, You will find our professional recommendation.
I hope it helps you!
Let’s go!


The German passive house institute doesn’t consider water harvesting since their standards are based on energy consumption.
However you may consider saving water as well as collecting water wherever you live since water will be a scarce supply soon.
Plus, why pay for the water when it comes free from the sky?

Fun facts:
Oslo in Norway is the most expensive water supply in the world (2021) with a cost of 6,69 €/m3. Then San Francisco (6,07 €/m3), Stuttgart (5,67 €/m3) in second and third place. From the first 10 of the list, 4 are in the United Estates: San Diego (5,38 €/m3), Indianapolis (5,17 €/m3), Seattle (4,60 €/m3) and Portland (4,55€/m3).

Most expensive water supply city in Spain is Barcelona with a cost around the 2,00 €/m3.
The next two cities with the most expensive water supply cost are Almeria (1,95 €/m2) and Madrid (1,65 €/m3).
Data taken from Statista.

Rainwater harvesting

In order to calculate the amount of tank that you need, first you need to consider diverse aspects like where do you want to use the rainwater (gardening, toilet tanks, cleaning and/or washing machine), amount of rainfall along the year (l/m2), number of people using water all year long, roof size, water price of your area and garden size.

Usually the most common is to use it for gardening only. It’s not very common to find home owners using rainwater for other uses like washing clothes in the washing machine or in the toilet tanks. The reason is the devices like washing machines and even toilet tanks could start having a lot of maintenance problems when run with rainwater. I still couldn’t find a water tank provider or a builder, or even a client that wants to try this in Spain. The reason is they don’t want to cover the risk of arranging the whole thing if it doesn’t work.

In most parts of Spain, rainwater doesn’t come constantly. It rains massively only three times a year and you need to collect all the year’s water harvest in those three moments. This also means you need bigger tanks to collect all the water you’ll use all year long. Most common for a 200m2 positive house is to have a 10.000l deposit. And even so, you’ll end up with a dry deposit sometime in summer. You may balance this with another type of water harvesting. Let’s see two types:


The price of one water harvesting deposit of 10.000litres of two of 5.000litres is around the 5.000€.
Mind you’ll also need to cover the installation price.
Also mind that this will not be enough to cover all your needs in Spain all year long, so you need to install also another deposit for either greywater harvesting or blackwater treatment.


Our professional recommendation:
For Spain we recommend having 3 deposits.
The first to collect water from roofs of 10.000l.
The second to collect and filter grey water of 10.000l.
And finally the wastewaters treatment deposit of another 2.000l that will cover the filtering of sewage for gardening for a house of 3 to 6 people.
That would give you enough water for irrigation of a garden for a 300m2 house and 800m2 of garden or horticulture.

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Hope this post ‘Rainwater harvesting in Spain and price’ is helpful!

Best of luck on this adventure.
See you on the next post,


Founder of ERA architects 

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By |2023-03-02T07:52:54+01:00January 7th, 2023|Passive House Architect Barcelona|0 Comments

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