> You'd have to dig a well to get a high enough level of arsenic to poison yourself.
Not so fast. Acute poisoning from above-ground sources may be unlikely, but chronic isn't unknown.
http://www.who.int/mediacentre/factsheets/fs210/en/
http://en.wikipedia.org/wiki/Arsenic_contamination_of_ground...
It's a lot more likely you'll die if you avoid drinking water.
What's this got to do with HN, in any case? 'Survival skills' for hackers is probably more akin to having to cook for yourself if the local pizza/mexican/chinese/whatever place is closed (to play on a stereotype; plenty of hackers are good cooks).
Hackers !== Code hackers
Arsenic is in all unfiltered water. You'd have to dig a well to get a high enough level of arsenic to poison yourself.
It is extremely unlikely you'll get sick from drinking boiled water taken from a stream. Sure, nothing is proof of safety. You could distill pure water and then accidently inhale some of it and dry drown.