A solar distillation apparatus utilizing a substantially vertical reactor assembly is disclosed. The reactor includes a tubular outer shell, a base, a cap, and a central tension member. The annular space between the outer tube and the central tension member forms the reactor chamber. Seawater or other feed liquid enters the reactor chamber through the base plate. Reflected or direct solar energy heats the feed liquid, generating low pressure vapor. The vapor exits the reactor through the cap structure or the base. The concentrate left behind settles by gravity to the bottom region of the reactor's liquid column. Extension tubes on the feed openings allow feed liquid to enter the liquid column above the concentrate layer and avoid excessive mixing of the feed liquid and the concentrate. The concentrate exits the reactor through one or more openings in the base.