You’re better off getting a water butt to collect the rain then running it into a filter
Not all water is the same. Donat is a great example of this. Jam packed full of Magnesium.. It tastes like an Alka Seltzer and probably turns your piss to stalactites if you drink too much of it. I'm turning into a fan though. Available in Lidl and probably your local Polski Sklep. 
https://en.m.wikipedia.org/wiki/Donat_Mg
Discussion
I swear I just don’t know