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. The total water amount from the calculator includes water from other foods and beverages that can contribute to fluid balance, including coffee and tea.
Maintaining water balance is essential for your survival. For this reason, your body has a sophisticated system for regulating when and how much you drink. When your total water content goes below a certain level, thirst kicks in. This is controlled by mechanisms similar to breathing — you don’t need to consciously think about it. For the majority of people, there probably isn’t any need to worry about water intake. The thirst instinct is very reliable.
However, certain circumstances may call for increased water intake. The most important one may be during times of increased sweating. This includes exercise and hot weather, especially in a dry climate. If you’re sweating a lot, make sure to replenish the lost fluid with water. Athletes doing very long, intense exercises may also need to replenish electrolytes along with water. Your water need also increases during breastfeeding, as well as several disease states like vomiting and diarrhea. Furthermore, older people may need to consciously watch their water intake because the thirst mechanisms can start to malfunction in old age.