Most people do not need to keep track of how much fluid they take in. The average person takes in 6-8 glasses of liquids each day without even thinking about it, just by following their own thirst sensations. They meet almost 80 percent of their needs for water by drinking anything liquid and get the remaining 20 percent from the food that they eat (Antioxidants (Basel), 2018 Apr; 7(4): 56). The Institute of Medicine of the National Academies reports that women take in an average of 12 glasses (2.7 liters or 91 ounces) and men take in the equivalent of 16 glasses (3.7 liters or 125 ounces) of water each day from drinking and eating.
Conditions that Increase Your Needs for Water
• Being overweight: More than two-thirds of your body weight is water, so heavier people need to take in more water
• Weather: the hotter the weather, the more you sweat
• Exercise: when you exercise, you sweat more and require more fluids
• Various diseases: for example, you lose fluids when you have a fever, vomit, have diarrhea, kidney stones, urinary tract infections, or conditions that cause excess urination such as diabetes. Dehydration can be caused by dementia when you forget to drink, or by diseases that interfere with thirst, eating or swallowing, or that make you urinate large amounts.
Symptoms of dehydration include a dry mouth, excess thirst, headaches, or muscle cramps. Suspect that you are not getting enough water when you are urinating infrequently or having dark yellow or even brown urine with a strong odor (Eur J Nutr, Aug 19, 2016;55:1943–1949). Urine usually should be pale yellow and clear (not cloudy).
Drinking Plain Water Regularly Can Help You to Lose Excess Weight
Drinking a glass of water just before you eat can help you to eat less and lose excess weight (Clin Nutr Res, Oct 2018;7(4):291–296). Several studies have found that filling the stomach with water leaves less space for excess food so a person feels full earlier and may eat less (Am J Clin Nutr, 1995;62:923–931; Am J Clin Nutr, 2004;80:656–667; Appetite, 2005;44:187–193; Eur J Clin Nutr, 1993;47:815–819). One study found that people who drink water before eating take in about nine percent less (194 kcal/day) than those who did not drink water (Obes Res, 2005;13:2146–2152). Drinking 6-8 glasses of water each day helped women to lose weight (J Nat Sci Biol Med, Jul 2014;5(2):340-4). Drinking plain water rather than drinks with sugar or artificial sweeteners can also help you to lose weight since liquid sugar is absorbed immediately from the gut to cause high rises in blood sugar, and even if the beverage contains no calories, the sweet taste can increase hunger (Appetite, 2005;44:187–193). See Drink Water Instead of Sweetened Drinks
Drinking Too Much Water Can Be Harmful
On rare occasions, a person can take in too much water. Examples include:
• People who suffer from conditions that cause the body to retain fluids, such as heart failure or kidney disease
• People with diseases that cause excess thirst such as those that damage the brain
• Novice athletes in long-term events such as marathons who spend more time drinking than pushing the pace. The excess fluids can dilute their blood so they develop low blood salt levels, which can be fatal. See Hyponatremia
Possible warning signs that a person is taking in too much fluid include:
• swollen fingers or feet
• muscle cramps
• excess fatigue
• nausea or vomiting
• confusion or irritability
• passing out
Most of us don’t need to count how much fluid we drink as we can meet our needs for fluids just by drinking when we feel thirsty. People with certain medical conditions, those taking certain medications, those in extreme climate conditions, and athletes in endurance events do need to take in extra fluids. If you feel you may not be getting enough fluid, check with your healthcare provider. Water is the most healthful drink, while all sugared drinks, including fruit juices, cause high rises in blood sugar to increase risk for weight gain and diabetes.