How exactly does a cactus live without water?

Well, it doesn’t live entirely without water. Every living thing requires water, but a cactus is just well-designed to survive without a lot of water, plus it uses what water it does have much more efficiently than other plants. Because it has no leaves, it doesn’t give up its water through evaporation as easily as other plants. Its stems are thick with a lot of room for storing water, and with a protective covering that keeps the stored water inside. Some cactus species can go for two years without water. The indoor varieties, however, do require more frequent watering, depending upon the species.