I have constructed several versions of the solar still, both in my days of working as a summer camp counselor and while teaching outdoor living skills as part of an after school program, and also at home. (It was something fun to show my kids) There are many methods that can be implemented with any number of items as long as you have the basics: something to seal in heat, something to condense the water vapor and a vessel to collect it. You don't even need to use sea water: You can dig a hole, bury a cup, can or jar at its center, pack fresh foliage around it and cover with a tarp, weighted at its center. (Ground still) The heat evaporates the moisture in the leaves, condenses on the tarp and drips to the center into the cup. This is one of many versions.
The problem with solar distillation, however, is that it can be a frustratingly slow process, even when you are evaporating sea water and not green leafies. When you are dying of thirst, it can be so tempting to open the tent to see how much water is collected. The second you do that, you have to start at the beginning. The still has to be left undisturbed for extended periods of time, usually several hours. The output varies widely depending upon the size and the method used and weather conditions. More than one still would increase water output but a limited amount of construction material can be prohibitive. Ground stills require a great deal of energy to construct and you often end up losing more water than you distill through perspiration. On a good day, with one still, you can expect between 1 and 2 liters. On a bad day, maybe a cup or two. Helpful but not likely enough to sustain two people in the Niku environment indefinitely.
I am very fortunate that I have never been in a situation where I actually NEEDED to build one, but I'm glad I know how. Looking at the Electra, I can see many parts that could be hammered off to make a solar still, among other survival equipment. However, someone had to show me how to build these things first. Until they did, it never would have occurred to me. Being a sailor, Fred might have known how to construct a still, but if he was dead or incapacitated, it would have been up to Amelia. Would she have known how? Would she be in any shape, physically? Would it have been enough?
Coulda, woulda, shoulda.