How can cacti live with very little water?

Cacti have an outer waxy layer and their leaves have evolved into thorns to prevent evaporation of water. In the morning, their thorns and the outer waxy layer are also able to absorb dewdrops. They store water in their bodies and roots and consume it slowly. The Saguaro cactus, a ribbed column cactus in the Mexico desert, fills itself up completely when it rains heavily and expands like an accordion.