Does your body run best on 8 glasses of water a day? Not necessarily. Everyone has different fluid needs. The weather--both temperature and humidity--plays a part and so does your size, gender, and level of activity. So, are 8 glasses of water a day really linked with good health?

Some say 8 glasses of water helps with weight loss. That wasn't true of 38 overweight and obese teens though, who were asked by researchers to drink more water for six months. Those researchers found no link between drinking 8 glasses of water and weight loss.

Others claim that drinking extra water beyond what you're thirsty for helps hydrate or smooth skin, reduces headaches, or helps flush more toxins from kidneys. These claims were carefully reviewed and found untrue: "There is no clear evidence of benefit from drinking increased amounts of water," the researchers concluded. Instead, this study found that drinking when thirsty is good enough for most people.