I have read any number of water purifier products and while many claims are made, the only real world user of a sawyer water filter which claims to remove "The MINI removes 99.99999% of all bacteria, such as salmonella, cholera and E.coli; removes 99.9999% of all protozoa, such as giardia and cryptosporidium".
The user and his friend became ill anyway.
Yes, boiling is best but is there another way ?
The SteriPen makes claims but again, does it really work ?