In order to take a short rest, your character needs to drink at least 16 fluid ounces say from a flask, or 'skin. Additionally drinking beer, grog, wine etc gives the character a d6 of temporary hit points that last until they take another short or long rest. Potent drinks and drugs may grant more temporary hit points. A flask holds 16 oz, while a waterskin holds 80 oz. Drinking befouled water will likely poison your characters... To take a long rest, your character needs to eat a meal. If you don't have anything to eat, you don't recover exhaustion, hit points or hit dice from the rest.