Why Is The Saguaro Cactus Called A Living Water Tank?

Because of the amount of water that this desert plant can soak up and store. You see, rain does not fall for many months in the desert. But when it does, the saguaro cactus will soak up enough water to keep living and bearing fruit and blossoms for a year or even longer. And when it is filled with water it can weigh five or more tons.
Close study of this cactus water tank tells us that it is ideally suited for its desert home. Rather than having a long taproot that could not survive in the desert sands, this cactus has long near-surface roots that spread out in all directions from its main stem. When it rains, these roots will take in water from the sand as fast as it falls. Also its "skin" or smoothly waxed outer shell is grooved to expand like an accordion when it is taking in water. Further, the inside of this waxy, watertight shell is filled with a spongy material that absorbs the water taken in by the roots.