Too bad about the ring saws. I thought one might fit the parameters but if they don't work at all I agree it's a waste.

FWIW - I was into survival type stuff as a kid and tried a few solar stills. It works but you don't get much. I probably sweat more digging various holes. Narrow and deep, the steeper is better rivulet wise but you'd have to be really thirsty.

Maybe Mylar would have less surface tension type beading properties. I used Visqueen or something. YMMV