I am not a survivalist, per se, but I love reading and collecting knowledge.
One of the really cool survival things you can build to purify water is a solar still.
http://sommerleigh.com/wp-content/uploads/2012/02/solar-still.gif
It’s a simple concept that in real life requires:
A sheet of plastic
A tool for digging
A bucket
Rocks
You dig out a hole of varying sizes and then secure a sheet of plastic above the hole with rocks. Then you place one rock in the center so the sheet sags down to where you’ve placed the bucket.
Basically the soil is heated by the sunlight passing through the plastic sheet, condensation collects on the plastic sheet and gathers in the bucket. Depending on the day and where you’ve placed it you can probably get a bottle of clean water a day from one.
So it wouldn’t be a complete solution to water needs but I think it would be a nice high end survival recipe that, by the time you can build one and passively gather water, it wouldn’t be game-breaking as much as it would be a convenience.