You can fill up containers by finding a well or fountain. If you are becoming thirsty it will tell you your throat is becoming parched. You will want to take a drink to prevent becoming thirsty. If you do become thirsty, you will not regen as fast, in fact you will hardly at all. If you abstain from drinking for a long period of time, you could die from thirst.
Eating also goes along the same lines as drinking.
You must eat in order to survive. When your stomach rumbles, you will want to get something to eat. You should have a few things of food at all times everywhere you go. This will show in order, your health percent, mana percent, and stamina percent. The numbers are percentages and are not actual figures.