Chuckwalla only obtain water from plants, find out why?

Chuckwalla is known as the predator of chickens in my coutry. It is a large, bulky lizard reaching nearly 16 inches (40 cm) with folds of loose skin on the sides of its body. You can find this species on arid, rocky hills of southern North America. They live on deserts  as they like heat. They don't move in the morning till the sun warms it to about 100 degrees. When this species gets too hot, they crawls into the shade but it can also change color to reflect more or less light and heat.All species of chuckwallas are predominantly herbivorous, eating a variety of desert plants, including leaves of the creosote bush. Chuckwalla

To identify the chuckwalla, they have stocky wide-bodied lizard with a flattened midsection and prominent belly. Their tails are thick, tapering to a blunt tip. It has loose folds of skin characterize the nest and sides of the body, which is covered in small, coarsely granular scales. Chuckwalla lays eggs, and friable, sandy, well drained soil is required for nesting. In years of less than average rainfall and low plant productivity, reproduction many not occur. This species can be active all year in warm areas but most activity occurs in spring and early summer. It is harmless to humans. The males are seasonally and conditionally territorial, and abundance of resources tends to create a hierarchy base on size with one large male dominating the area's smaller males. To identify males from females, makes having reddish-pink to orange, yellow or light gray bodies and black heads, shoulders and limbs, females and the immature have bodies with scattered spots or contrasting bands of light and dark in shades of gray or yellow. Remember this too, males are generally larger than females and possess well-developed femoral pores located on the inner sides of their thighs. The pores produce secretions believed to play a role in marking territory. This species obtain all their water from the plants they eat and never drink, even when water is readily available.