6. Yellow urine is a sign of dehydration.

Myth. It can be, but not all yellow urine is cause for alarm. “Dark yellow urine may be a sign of dehydration,” says Zuckerbrot. “The kidneys filter waste products and reabsorb water and other useful substances from the blood, so they control the volume and concentration of urine output. Dehydration leads to increased urine concentration, turning your urine dark yellow. Ideally your urine should be straw yellow in color.” Other factors, though, such as taking a multivitamin, can also lead to yellow urine.

7. If you’re thirsty, you are already dehydrated.

Myth. If you start to feel thirsty, then you are headed in the wrong direction and should grab a drink of water, but thirst doesn’t necessarily mean you’re dehydrated. “Thirst begins when the concentration of [substances in the] blood has risen by less than 2 percent, whereas most experts would define dehydration as beginning when that concentration has risen by at least 5 percent,” notes Hess-Fischl.

8. You need sports drinks, not water, to function at a high level in athletics.

Myth. Sports drinks may have fancier advertising campaigns, but water is really all you need to get the fluid necessary to participate in most athletic endeavors. “Adequate fluid, especially water, is most important for athletes of all ages as it is the single most important way the body has to transport nutrients and energy and remove heat during exercise,” says Chavent. “A sports or vitamin beverage may taste better, but is not necessary for hydration and is expensive.” Keep in mind though that people who run marathons or compete in highly strenuous activites may need to supplement their water intake with sports drinks to offset the salt they lose due to heavy sweating over long periods of time. This doesn’t apply to most people who are simply exercising to get fit at the gym, for instance.

9. It’s possible to drink too much water.

Fact. People with certain health conditions can put themselves at risk of complications if they drink too much water. “People with some heart conditions, high blood pressure, or swelling of the lower legs [edema] need to avoid excess water,” says Hess-Fischl. “If you have a history of kidney problems, especially if you have had a transplant, consult your doctor before increasing your fluid intake.” Hess-Fischl adds that you shouldn't drink too much water while eating, as it dilutes your stomach acid and can cause digestion problems.

10. You should not reuse plastic water bottles.

Fact. Plastic water bottles can present a couple of risks to people who drink their contents and then fill them up time and again. “These bottles leach chemicals into your water after multiple uses,” Hess-Fischl explains. “The bottle, if not properly cleaned, may also harbor bacteria from your mouth.”

Water is essential to survival — use these facts to figure out if you need to increase your intake or feel reassured that you’re drinking enough.