Hi Racman-Hope you are well,
This is a very interesting topic as well as a vast one. Potable pure drinking water these days is just about impossible to find anywhere.
Most people think that there is an endless supply but they couldn't be more wrong. Just turn the handle on your faucet and you've got clean water right?...Not really.
In my spare time when I'm not drumming, I am a survivalist. No I'm not a lunatic crazy person, but someone that doesn't take things for granted. Like water.. There are literally millions that die every year on this planet from simply not having any. And even more that die from drinking water riddled with contaminants. Granted these are people living in countries that are not as developed as ours, but none the less-they don't have clean water.
If you really want 99.9999% absolutely clean drinking water, I would suggest getting water out of your faucet, (because it's the same water they use in the plastic bottles you buy, minus the chemicals from the plastic). Boiling it first- then running it through a filtration system (see link)
http://www.katadyn.com/usen/These Katadyn filtration systems are some of the best made that I've discovered in my research- if not the finest.
once you boil your water, let it cool, then run it through the Katadyn, put it in a thick glass container. You won't get the chemical run off from the plastic, or the chlorine and flouride treatments to the water that you get coming out of your faucet.
I could go on about water because it is such a vital part of our lives, and without it- we die. I believe one day water will be more valuable than gold and silver. Oh and please don't make the mistake of thinking if you find a clear spring or stream that the water is good to drink.
Definitely not the case. Hope this helps in some way. You wouldn't believe what's in our water..it's scary.