Like humans and animals, plants need both water and nutrients (food) to survive. Most all plants use water to carry moisture and nutrients back and forth between the roots and leaves. Water, as well as nutrients, is normally taken up through the roots from the soil.
So, for example, a 3-month old puppy should be able to hold its urine for approximately 4 hours in a pinch. This means that if you have a properly toilet trained 4-month-old puppy that, theoretically, can hold its urine for 5 hours, and you shut that puppy in a crate for 6 or 7 hours, you are courting disaster.
Even if you're crating your puppy for three hours, she'll need an opportunity to move around and to relieve herself. As a general rule of thumb, puppies are able to control their bladders for one hour for every month of age. For example, a 4-month-old puppy can usually hold in her pee for a maximum of four hours.