How much water should one drink in a day?

Many factors dictate how much water (fluid) you should drink per day. Examples include: your overall health, your sex, age, total daily activity and the environment that you live.

Water is your body’s main chemical component, comprising approximately 60% of your total body weight. Each of your body’s major systems depend on water; it helps control your body temperature, it helps carry essential nutrients to your cells, helps flush out toxins from organs and can help keep your ear, nose, and throat moist. Dehydration can result if your body does not have enough water. Many of my patients getting treatment for cancer struggle with dehydration. Chemo/radiation related side effects (nausea, low appetite, diarrhea, etc.) can make eating difficult and may lead to dehydration. Common signs of dehydration include: fatigue, headache, dry mouth, little or no urination, muscle weakness, and dizziness.

Water is lost through breathing, sweating, urinating and having bowel movements. The average urine output is about 1.5 L per day and you also shed an additional liter through breathing, sweating, and bowel movements. The Institute of Medicine suggests:

Men = consume roughly 3.0 L (13 cups) of total beverages per day Women = consume 2.2 L (9 cups) of total beverages per day

Fluid intake should consist of water, milk, juice, sports drink or other beverage other than alcohol. For a while, some professionals did not include caffeinated beverages into one’s daily fluid intake. But, caffeine does not have the same diuretic effect on someone who is used to drinking it often, so now some professionals feel that it can be counted towards fluid goals (with a limit at ~3 cups a day). On average, food provides about 20% of total water intake. Also keep in mind that foods contain fluid as well. A diet high in fruits and vegetables can definitely contribute towards “fluid” intake.

There are many factors that influence water needs. For each hour you exercise, you should consume about 2-3 cups of water (depending on how much you sweat). If you live in humid weather or at altitudes of greater than 2,500 meters, it is recommended that you increase your fluid intake. Signs of illness such as diarrhea, vomiting, fever, etc. call for an increased fluid intake. Breastfeeding women should also consume approximately 12.5 cups of fluid a day.

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