It is the bitterest of ironies that a snake which spends its entire life at sea, constantly submerged in water, should spend months on end being thirsty and dehydrated.

Fresh water quenches thirst. Salt water worsens it. If you drink seawater, your kidneys try to get rid of the excess salt by diluting it in urine, and you expel more water than you take in. The same applies to other land animals, and those that return to the sea have special adaptations for coping with salt. Many sea animals avoid swallowing seawater entirely, and get fresh water from the food they eat. Turtles, sea birds and marine iguanas have special glands for getting rid of salt.

Sea snakes have similar glands