1. Is pretty easy:
I am a delegate of the federation of the red cross and red cresent movement and I am a Wat/San technician.
If you just want to get viruses and bacteria out (without reverse osmosis toxins etc. is not even possible) there is nothing better than this one:

http://www.amazon.com/Katadyn-80136...07U00YE/ref=cm_cr_pr_product_top?ie=UTF8

And it does 13.000 gallons!