Because you are constantly losing water from your body, primarily via urine and sweat. To prevent dehydration, you need to drink adequate amounts of water.

There are many different opinions on how much water you should be drinking every day.

Health authorities commonly recommend eight 8-ounce glasses, which equals about 2 liters, or half a gallon. This is called the 8×8 rule and is very easy to remember.

However, some health gurus believe that you need to sip on water constantly throughout the day, even when you’re not thirsty.

As with most things, this depends on the individual. Many factors (both internal and external) ultimately affect your need for water.

Many people claim that if you don’t stay hydrated throughout the day, your energy levels and brain function start to suffer.

And there are plenty of studies to support this.

One study in women showed that a fluid loss of 1.36% after exercise impaired mood and concentration and increased the frequency of headaches.

Other studies show that mild dehydration (1–3% of body weight) caused by exercise or heat can harm many other aspects of brain function.

Keep in mind that just 1% of body weight is a fairly significant amount. This happens primarily when you’re sweating a lot.

Mild dehydration can also negatively affect physical performance, leading to reduced endurance.

Mild dehydration caused by exercise or heat can have negative effects on both your physical and mental performance.

Plain water is not the only drink that contributes to your fluid balance. Other drinks and foods can have a significant effect.

One myth is that caffeinated drinks, such as coffee or tea, don’t help you hydrate because caffeine is a diuretic.

In fact, studies show that the diuretic effect of these beverages is very weak.

Most foods are also loaded with water. Meat, fish, eggs and especially fruits and vegetables all contain significant amounts of water.

For more ideas, check out this article on 19 water-rich foods.

Together, coffee or tea and water-rich foods can help maintain your fluid balance.

Other beverages can contribute to fluid balance, including coffee and tea. Most foods also contain water.