Water is your body's principal chemical component, comprising, on average, 60% of your weight. Every system in your body depends on water. Every day you lose water through your breath, perspiration, urine and bowel movements.
Lack of water can lead to dehydration, a condition that occurs when you don't have enough water in your body to carry out normal functions.
Though uncommon, it is possible to drink too much water. Too much water consumed causes hyponatremia, a condition where there is insufficient sodium in the blood.
According to Mayoclinic.com there are several approaches attempt to approximate water needs for the average, healthy adult living in a temperate climate.
- Replacement approach. The average urine output for adults is about 1.5 liters (6.3 cups) a day. You lose close to an additional liter of water a day through breathing, sweating and bowel movements. Food usually accounts for 20 percent of your total fluid intake, so if you consume 2 liters of water or other beverages a day (a little more than 8 cups) along with your normal diet, you will typically replace the lost fluids.
- Eight 8-ounce glasses of water a day. Another approach to water intake is the "8 x 8 rule" — drink eight 8-ounce glasses of water a day (about 1.9 liters). The rule could also be stated, "drink eight 8-ounce glasses of fluid a day," as all fluids count toward the daily total. Though the approach isn't supported by scientific evidence, many people use this basic rule as a guideline for how much water and other fluids to drink.
- Dietary recommendations. The Institute of Medicine advises that men consume roughly 3 liters (about 13 cups) of total beverages a day and women consume 2.2 liters (about 9 cups) of total beverages a day.
Even apart from the above approaches, if you drink enough fluid so that you rarely feel thirsty and produce 1.5 liters (6.3 cups) or more of colorless or slightly yellow urine a day, your fluid intake is probably adequate.
However, you may need to modify your total fluid intake depending on how active you are, the climate you live in, your health status, and if you're pregnant or breast-feeding.