Interesting article, worth reading, but on top of the list I would have put a water filter as number one.
You need to drink everyday (quantity depends on climate). Otherwise, you start having problems with your kidneys.
And 3 days without drinking, you've got very serious medical problems!
I also like the Lifestraw
https://goo.gl/5BTG2W this filter got a LOT of good reviews (marketing ? may be... but the specs are really good) and I used it a few times and it works really well
Now, regarding the price in this article, you can get much cheaper