This has been submitted by Cava3r4:
I don't believe you could mix enough in water to "purify" it.
Porter beer was made back in about the 1500s as a solution to purifying a liquid to make it safe to drink. Porter beer was sometimes called "a meal in a bottle."
Beers in general range from near-beer 1/2 of one percent to generally 9-10 percent (above that level and it becomes barley wine).
I'm pretty sure the reason the Porter Beer was safe to drink is the fact that during the process of making it, the water (wort) is boiled for at least an hour which in itself purifies the water.
PS. I am a home brewer.