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.
A general guideline is that a 5 month old Maltese puppy can wait about 5 hours and a 6 month old Maltese can hold on for about 6 hours and so on. However, the longest amount of time a dog can be expected to hold their urine or bowel movements is 8 hours. To expect more than that is to go against Mother Nature.