You can survive for a LONG time without food, depending on your fat stores, but you can only last a couple of days without water. What happens when you do? This video from SciShow explains the gory details.
Most diets recommend that you drink 6-8 glasses of water a day to keep hydrated, which is a good idea considering that many people turn to food when they’re actually thirsty. So remember to drink your water so you don’t get dehydrated.