I want to harvest rain but I live in a town close to Paris, in a small appartement, with no personal garden and only two windows with a small balcony fence.

I thought about hanging a rain gutter connected to some kind of small water tank (like a bottle) beneath it.

Before doing it let's try to calculate how much water I can harvest over a year with such a system.

According to some random website we get an average of 650 mm of rain over a year in my area. The dimensions of a rain gutter are about 100 mm width and 1000 mm length considering the size of my windows. Just with the surface of the rain gutter that's about 65 L of water over a year. That's way more than what I expected and I can double that if I use both windows.

So, the project looks viable and I will have to design it so that the water tank is easily removable. That way I can use a bigger secondary water tank and not have 10 L or more hanging on my old balcony fence.

Did I miss anything or did it wrong ? If so, tell me in the comments.