For something so seemingly simple and essential as drinking water, plenty of myths and misconceptions exist about possible water benefits and harms.

Learn how to separate the myths from the facts about drinking water.

1. Everyone needs to drink eight glasses of water a day.

Myth. Though water is the easiest and most economical fluid to keep you hydrated, the latest Institute of Medicine recommendation is that women should strive for about two liters or eight glasses a day and men should aim for three liters or 12 glasses a day of any fluid, not just water. “No one can figure out where this ‘eight glasses of water’ came from, but I believe it came from the old RDA [recommended daily allowance] for water that matched water requirements to calorie requirements,” notes Georgia Chavent, MS, RD, director of the Nutrition and Dietetics Program at the University of New Haven in West Haven, Conn. “The new requirement from the Institute of Medicine is much more generous and includes recommendations for total beverage consumption, not just water.”

2. Drinking water flushes toxins from your body.

Fact. Though water doesn’t necessarily neutralize toxins, the kidneys do use water to get rid of certain waste products. If you don’t drink enough water, your kidneys don’t have the amount of fluid they need to do their job properly. “If the body does not have sufficient water, then metabolic wastes will not be removed as efficiently as they should,” explains Amy Hess-Fischl, RD, CDE, of the University of Chicago Kovler Diabetes Center. “In essence, the body would be holding in toxins instead of expelling them, as is required for proper health.”

3. Bottled water can cause tooth decay.

Myth. Bottled water in and of itself doesn’t cause the teeth to decay, but it usually doesn’t contain any fluoride, which is added to tap water to help prevent tooth decay. “Fluoride is an important element in the mineralization of bone and teeth,” says Constance Brown-Riggs, RD, CDE, author of The African American Guide To Living Well With Diabetes and a nutritionist and certified diabetes educator in New York City. “With the increased consumption of bottled water, which is not fluoridated, there has been an increase in dental caries [cavities].”

4. Drinking water can help keep your skin moist.

Myth. While it used to be believed that staying properly hydrated led to youthful, vibrant skin, the reality is that the amount of water you drink probably has very little to do with what your skin looks like. “Unless the individual is severely dehydrated, drinking large quantities of water will not prevent dry skin,” Hess-Fischl says. “Basically, the moisture level of skin is not determined by internal factors. Instead, external factors such as skin cleansing, the environment, the number of oil glands, and the functioning of these oil-producing glands determine how dry the skin is or will become. The water that is consumed internally will not reach the epidermis [the top layer of the skin].”

5. Drinking water helps you lose weight.

Fact. Drinking water won’t specifically trigger weight loss, but it can aid in the process. Water replaces other calorie-laden beverages in the diet, causing you to reduce your overall number of calories. Plus, it can make you feel fuller, so you may eat less at each meal. Water, particularly cold water, may even play a role in increasing your metabolism. “A new study seems to indicate that drinking water actually speeds up weight loss,” says Tanya Zuckerbrot, MS, RD, owner of Tanya Zuckerbrot Nutrition, LLC, in New York City. “Researchers in Germany found that subjects of the study increased their metabolic rates [or the rate at which calories are burned] by 30 percent after drinking approximately 17 ounces of water.”