If we lost access to electricity, we'd be completely screwed; we can't even get drinkable water in many places without electricity.
For example where I live there is water around 10-20m depth, but it's polluted (it may be usable for agriculture but not for human consumption); you'd have to dig a well over 100m below the surface.
Boil it
The standards for what is fit for human consumption might drastically change in a post-apocalyptic scenario, though.