Earthship Belgium vzw

May 16, 2010 (last revised on October 25, 2011) - Because of my inquisitive nature, I wondered why in European earthships (Ger, Oscar and Lisa) usually two barrels of 5000 liters are used for water collection.

Would this be enough or would you have to deal with periods of insufficient water supply?How much water actually falls from the sky in Belgium? How many liters a year do we use? How many liters can we collect? Question after question after question arose from me. Fortunately, there is the internet and with some patience you will soon find a lot of answers..

Reception capacity

The first step is to determine how much rainwater we can collect. There are 2 important factors: the amount of precipitation per m² in a given time interval and the surface that you collect your water from (in case of earthship, this will be your roof) Once you know these factors, it's easy to calculate the maximum of what you could harvest.

After some investigation I found the data on the website of KMI, measured over a period of 30 years (1971-2000). It is the average monthly rainfall. For the Dutch situation, you can visit the website of KNMI.

Source: KMI

The figures are in mm. It is as follows: 60 mm per month equals 60 liters per square meter per month.

Surface of the water collector.

In an earthship the roof is used as a water collector. This requires you to use waterproof materials that do not contaminate the water like eg. EPDM

Now each earthship will differ in size and therefore the capacity to water harvest. Hence we assume a 2 bedroom, 1 big kitchen, bathroom, toilet, a washing-/system space, conservatory, front and rear hallway. This is most certainly achievable on 200 m², which is also your roof area.