There is only a little bit of truth to the widespread advice to drink eight glasses of water per day.
Instead, people should aim to consume an amount of liquids tailored to their lifestyle and personal needs.
How much people exercise and lose fluids through sweat, the medications they’re taking (including diuretics) and age are examples of the factors determining how many glasses they should drink per day.
In 2004, the Institute of Medicine came out with guidelines and reassured the majority of the population they can rely on their thirst as their guide, said Megan Ellison, a registered dietitian for Swedish/Edmonds.
The Institute advises men to consume 3.7 liters and women 2.7 liters of fluids per day, including foods as well as glasses of water.
Ellison instructs her patients to drink 1 milliliter of water per calorie they consume. So, for someone who consumes 2,000 calories per day, they should drink 2 liters of water.
For her patients who lead active lifestyles, Ellison says to drink two to three cups of fluid per pound lost.
The U.S. Department of Agriculture recommends reaching for water or milk as healthy options to stay hydrated.
When water just won’t do, the USDA advises drinking pop and juices in moderation and avoiding fast food restaurants’ super sizes.
Staying hydrated leads to a variety of health benefits.
Drinking water moves waste through one’s system, helps the immune system fight off sickness, and prevents such symptoms of fatigue as headache, back pain and dizziness, according to the Live Strong website.
Warding off dehydration with water leads to softer skin, regulated body temperature and helps people who are losing weight quench their thirst without adding calories.
Most people feel thirsty after losing 1 percent to 2 percent of their body weight in fluids, Ellison said. A person is considered clinically dehydrated after losing 5 percent.
Athletes, children and the elderly shouldn’t rely on their thirst. Athletes could see a drop in performance. The elderly and children typically ignore thirst cues, and children don’t have the cognitive thinking to know the consequences of getting too thirsty.
Ellison teaches her patients to stay in tune with their bodies’ needs.
“If we’re not in tune with our thirst cues, we think we’re hungry instead,” she said.
While Ellison recommends reaching for water to ward off dehydration, it’s appropriate to reach for a sports drink if you’ve been exercising for 60 minutes or longer to replace electrolytes. Hydration also can come in the form of coffee, milk, juice and fruits like watermelon and cantaloupe.
In general, 70 percent to 80 percent of fluid intake comes in fluids, 20 percent to 25 percent from fruits and vegetables, and about half a liter is made internally, Ellison said.
There’s no hard-and-fast formula for how much water you should take in each day. Follow your thirst and drink at meals, and you should be OK. If you need some rough guidelines:
START: 11 cups
IF YOU’RE A MAN: Add 4.5 cups
EXERCISING FOR AN HOUR: Add 2 cups
IF PREGNANT: Add 1.25 cup
IF BREAST-FEEDING: Add 4.5 cups
Sickness, heat and other factors also can increase the amount of fluids you need. All sources can contribute to total water needs: beverages (including tea, coffee, juices, pop and drinking water) and moisture found in foods. Moisture in food accounts for about 20 percent of total water intake.
Sources: Institute of Medicine, Mayo Clinic