How Much Water Do You Really Need?

We hear it all the time: We should drink eight 8-ounce glasses of water per day. But is this fact or fiction?

How Much Water Do You Really Need?
How Much Water Do You Really Need?

We hear it all the time: We should drink eight 8-ounce glasses of water per day. But is this fact or fiction?

There are no good scientific studies to support the eight-by-eight rule. The origins of this recommendation date back to 1945. The original guidelines actually came from a misinterpretation of a recommendation from the Food and Nutrition Board. The recommendation stated that a person should have 1 ml (about 1/5 of a teaspoon) of water for each calorie he or she consumes. The average diet at the time was approximately 1900 calories, meaning you needed about 64 ounces of water per day.


Now the Institute of Medicine sets general guidelines for total water intake. It recommends that women consume a total of 91 ounces (that’s about 2.7 liters) per day – from all food and beverages combined. For men, it’s about 125 ounces a day (or 3.7 liters). Depending on your diet, about 25% of the water you consume comes from your food.

Most of us healthy folks get enough water in the foods and liquids we consume. That includes any liquid we drink – even caffeinated beverages like soda, coffee and tea. Our kidneys work to perfectly balance and regulate our water requirements so that we take in and retain as much fluid as we need. Healthy people can let thirst be their guide to their fluid requirements.

However, certain medications – such as those for the heart disease, stomach ulcers or depression – can alter your thirst mechanism. So can certain diseases, like diabetes insipidus. The elderly can also sometimes have a poorly-regulated thirst mechanism. Another group of individuals that may require more fluids are people who have problems with kidney stones or chronic urinary tract infections. They may to need to over-hydrate from time to time and may benefit from excess water to flush out their kidney stones or bacteria from their bladder. Meanwhile, patients on dialysis for kidney disease may have to restrict their fluid intake.

Athletes, military recruits, or anyone forced to work outside during the hottest part of a summer day may require more fluids than generally recommended. And if you’re already in the throes of heat illness or heat stroke, you may have an inadequate or malfunctioning thirst mechanism.

But for most of us, an easy way to gauge how well-hydrated we are is to simply look at our urine. It should be fairly clear, and if it is very dark yellow, that’s sign we may need to drink more water.

Q: I end up overeating because it makes me feel better and I never really get full. I'd like to lose weight but this makes it hard. Any suggestions?

A: Being persistently hungry can cause big trouble. So can overeating for comfort/pleasure. These two behaviors, say researchers from Baylor University's Children's Nutrition Research Center, are controlled deep within your brain by serotonin-producing neurons, but operate separately from each other — one in the hypothalamus, the other in the midbrain. They both can, however, end up fueling poor nutritional choices and obesity.

Eating for Hunger

When hunger is your motive for eating, the question is: "Does your body know when you've had enough?" Well, if you are overweight, obese or have diabetes you may develop leptin resistance and your "I am full" hormone, leptin, can't do its job. The hormone's signal to your hypothalamus is dampened, and you keep eating.

Keep Reading Show less