Intro to distilation
http://lorien.ncl.ac.uk/ming/distil/distil0.htm

How it is done on submarines
http://www.fleetsubmarine.com/fresh_water.html

Solar Stills
http://www.txses.org/epsea/stills.html
http://www.thefarm.org/charities/i4at/surv/sstill.htm
http://www.rotarnet.com.au/users/9/9520/SolarWater/swp.html
http://www.davesplanet.net/solarstill/

If you would like them I have several links to building stills. These are primarily for alcohol but can work the same to purify water.
_________________________
When in danger or in doubt
run in circles scream and shout
RAH

And always remember TANSTAAFL