With the nearest water connection more than 500m away and crossing a main road plus multiple neighbours’ grounds, we decided to go for a rainwater collection and filtration solution.
So be prepared for a lot of numbers in this post.
In order to size such a system, I first tried to find out the demand of (drinking) water we would have on our plot.
According to a publication of the german Umweltbundesamt every person in Germany used 123l of drinking water per day.
This breaks down to the following parts as seen in the following picture:
I adjusted the numbers slightly to what I would expect in our environment (for example, as we are using a composting toilet we need nearly no water for the toilet, but I left in the 9% for small enterprises). Percentages in green are estimated less than the provided statistics and percentages in red estimated higher than the statistics:
This gives us a distribution like this:
I then calculated the demand for 2 people of several periods of time:
So I came to the conclusion that our 2 people household would roughly need 50’000l of drinking water per year and that with a standard 1000l IBC we could last approximately 7 days (which I the amount of water we can easily carry in one go with the TeleHandler).
I then went on to the SEPA web site to find information about rainfall data in the area where we are. Unfortunately, the nearest data points on their map are either Halkirk near Thurso or Kilphedir near Helmsdale.
Among the various statistics they provide they list the actual rainfall in mm/cm2 for the last 12 months:
I projected the numbers from this chart to the size of the roof of our barn (roughly 310m2) that would act as our water collection surface:
So even during the last driest months in the last year (June: 8’520l and March: 6’240l), we expect still be more than enough rain (> 4’000l) to supply us with water.
And now to the sizing: As I do not want to empty the tanks completely (there is always some sediment or dirt at the bottom of the tank), I want to be able to leave approx 20cm water level in the tanks.
I looked at the dimensions of water tanks from different suppliers and found these dimensions for the sizes of 5’600l, 7’200l, 10’000l:
So even with a 5’600l tank I could “survive” for a whole month and still had left 20% for increased demand while always leaving 20cm of the water in the tank. And with a lifting capacity of at least 1’250kg we can still move around such a tank if required.
So my sizing conclusion would be to get two of these 5’600l tanks (so one tank could always go into maintenance or act as a backup) and and have two 1’000l IBC tanks for emergency water transport.
Depending on the water tanks and its certification this would cost approx 2’500,00 GBP (without delivery fees or hoses and the like).
Did I miss or forget something? What do you think?
ps – below you find the podcast version of this blog post:
Our Journey to Scotland 