Passive solar still (basin distillation) — the simplest, most durable, most area-hungry option

A black-lined basin of saltwater under a sloped glass cover: sun evaporates the water, it condenses on the glass and runs off as distillate. No moving parts, no consumables, repairable with local materials — but output is ~4–6 L/m²/day, so area demand is the binding constraint.