Solar Trough for distilled water.

 I only drink and cook with distilled water!!

I would to build a solar trough capable for making a few (5) gallons per
day.  do you know of any sites that give a good example of the math, i.e.
size to focal etc,

my idea is to build one about 8 feet long, run a copper pipe along focal
point and feed water in at a rate that it would flash to steam, condense
steam.

Any idea as to size etc.  is 8 feet long enough??

any help appreciated.

ps; I have a good auto cad operator (wife)