Any random person you pass by on the street is unlikely to hurt you or harbor negative feelings toward you in particular, is unlikely to attack you if approached, and will most likely help in an emergency.
Sure they would. On average, you'd have to drink 13+ times per day, every day, for 80 years straight, to get killed by such tap water. There are plenty more things in life with worse risk profiles (e.g. cars, like 'unionpivo mentions).
Read a little of The World Until Yesterday by Jared Diamond and you'll get some surprising answers to this question. tl;dr in many places people who couldn't prove consanguinity would essentially have to attack each other due to a prisoner's dilemma dynamic. The idea of seing a stranger and just walking past them is actually quite new.
