Some plants, especially some species of cactus, contain water in a form that can be tapped and drunk directly. More often, however, the moisture in a plant cannot be obtained by any method other than the use of a still, which can retrieve water from the air. Water can be added to the surrounding air by placing plant parts in the still (but outside the area for capturing the pure water). A simple still can be constructed of plastic sheeting, some rocks, and a cup. Simply dig a hole deep enough to hold the cup, with a couple of inches to spare. The wider the still, the better, since it will have more surface area for water to condense on. Place the cup in the center of the hole and cover the hole with plastic (clear plastic is better than opaque, since it absorbs less heat). Use rocks to secure the edges of the plastic and place a small rock in the center of the plastic sheet to pull it down so that water condensing on the plastic drips into the cup. Such a still does not produce enough water for a person to live on indefinitely, but even a little bit of water can improve one's chances of survival.
Drinking alcoholic beverages will slake your thirst temporarily, but due in part to the diuretic nature of alcohol, will leave you more dehydrated than before. Since alcohol is a poison, the liver aggressively removes it, and a lot of water in the process. If alcoholic drinks are all you have, then try to heat the drink to above 60 °C for a short time to boil off the alcohol. Since alcohol has a lower boiling point than water does, it evaporates first.
Drinking saltwater will lead to water being drained from the body, because of osmosis.