Thanks for the great question!

All life on earth depends on water to survive. For plants, water is very important because it is needed for photosynthesis, or the transformation of sunlight into sugar used for food by the plant.

Some plants, however, are better than others at using less water to grow tall. Cacti, for instance, are adapted to use very little water due to the dry environments they grow in. To grow tall with less water, cacti have thick stems that store water and different type of metabolism for using less water to photosynthesize.

So all plants need some water to keep growing, but depending on the environment they can evolve ways to use water more efficiently.