How do you collect water with a tarp?

Sunlight distiller: in the arid desert area using the following method can be better collected to water: in the relatively wet ground dug a relatively wide 90 cm, 45 cm deep pit, the bottom of the pit in the center of a water collector, the pit surface hanging a plastic film pulled into an arc. Light can raise the temperature of the moist soil and air in the pit, evaporation produces water vapor, water vapor and plastic film in contact with condensation condensed into water droplets, sliding down to the vessel.