You could survive for many days without food, but without water you would die more rapidly. The human body is 60–70 percent water, which needs to be replenished constantly.
Water is responsible for transporting nutrients, gases, and waste products, and for regulating your body's temperature. It is not only vitally necessary for good health, it has side benefits of being able to cool or heat your body as well as moisturize and soothe your insides (and skin). It can also help you feel full and curb your appetite.
Drinking Enough Water
It was once thought that there was no limit to the amount of water you could drink in a day, but recently there have been alarming cases of hyponatremia — of drinking too much water. That said, chances are slight that you will drink enough water in a day to experience this. Most people drink well under the recommended daily amount of water for adults, which is 64 ounces.
The truth is, most people don't drink enough water. They're more accustomed to drinking soda, juice, coffee, tea, and alcohol. How often have you heard that you'll feel better just by taking in your 64 ounces of water every day? Well, it's true.
Hydrating Versus Dehydrating Fluids
You could argue that since many beverages are made with water, they should count toward your daily 64 ounces. This depends on the type of beverage. Hydrating beverages, all of which contribute to an improved functioning of your body, include (besides water) sports drinks that replace electrolytes; fruit juices (the less sugar, the better); soy or rice beverages (good whole milk replacements); herbal teas; and milk.
It doesn't help to cheat here, though. Milk may be hydrating, for example, but it's not a good idea to drink much more than 16 ounces of it a day, particularly if whole milk. And although juices do contain fruit, most readily available juices have sugar as their main ingredient (a simple carb that will lift you up and drop you down).
Dehydrating fluids contain water, but they also rob your body of water. These are caffeinated and alcoholic beverages. To minimize their effect, drink water with them in a 1:1 ratio.