I live in the US, in arguably the richest county in the US, per capita (Fairfax, VA).
Even so, there are times when no amount of money can make potable water come out of my tap. System flaws (e.g., water main ruptures), acts of God (e.g., hurricanes), or acts of man (e.g., sabotage) can all mess with the availability and/or quality of my water.
Not cool. Thirst, dysentery, and cholera are nasty things.
I'm loving the magnitude of water storage possible with common 55-gallon drums and PVC pipe or hose and hose fittings.
But if I had an infinite supply of water, I'd still have to purify it.
I have my solar oven, with a 'water pasteruization indicator (WAPI),' a little vial filled with soy wax. You put it in a container of water with the wax side up - come back after a day in the sun, and if the wax has melted and re-coalesced at the bottom, you know the water was at 200 degrees Fahrenheit for at least 10 minutes and has been pasteurized.
But I think I've come across something even better: The BioSand Filter. One of these babies can produce 5-15 gallons of clean water in an hour. Here are two videos: a funny one that doesn't really explain the physics/biology of the thing, and an earnest Christian charity one that does a great job of explaining all the details you need to understand:
Wikipedia has a nice article on the BioFilter, and there's a website called BioSandFilter.org that gives details regarding who, how, and what, for those of you who like those kinds of details.