I do not know about rain water, someone commented that if you collected it, and allowed it to sit for two days, the solutes would separate, but I have not looked into it. Walmart sells a gallon for 88¢, which works out to 0.255€/l.
Wait, you guys are weird: 0,255€/l.
I read a post by someone that was going through two gallons a day (7.5l), they bought this:
http://smile.amazon.com/Megahome-Cou...team+distiller and calculated that, taking into account electricity usage, they broke even in ten months.
Or you could do something like this:
How to Distill Water.
The floating glass bowl sounds weird. I would just put something under it and if I used enough distilled water, I might just dedicate a pot to it, and have a funnel run through a hole in the side.