Do You Really Need 8 Glasses? Maybe not!

Very few people question the importance of water in a healthy diet, but lately the needed quantity has been called into question.

The conventional wisdom of eight, 8-ounce glasses a day has been tossed aside, leaving one to wonder what food group myths might topple next.

The apple-a-day thing? The medicinal aspects of Mom's chicken soup?

"There has been research out there for a while that the eight, 8-ounce glasses a day has no research to back up it at all," Food Network dietitian Ellie Krieger told CNN.

"People just latched onto this number because it was really easy to remember. And I think people feel that if they're not drinking eight glasses of water, then they are not doing well for their bodies, and that is not necessarily true. "

But what is true is that our bodies are made up of a good deal of water. It makes up on average 60 percent of our body weight. And it seems to enable our basic functions.

Not only does it moisten tissues -- such as those around the mouth, eyes and nose -- it also cushions our joints, regulates our body temperature, helps our bodies get nutrients, and flushes out waste products.

Whew, talk about multitasking! 

But if the rule of eight is out, how do we know we're getting enough to keep us flowing?

"The general guideline is to pay attention to your thirst," Krieger said. "Your thirst is actually a good guide of how well hydrated you are and if you drink according to your thirst, you will stay hydrated."

She also had more good news: Liquids other than water count.

"So if you drink coffee or tea, even if it's caffeinated, it counts towards hydration," she said. "So do fruit juices and milk and soups and things like that."

Less caffeine -- which can dehydrate -- is better than more, in the fluid count.

Krieger says a good rule of thumb for moderately active women in temperate climates is that they need about nine 8-ounce glasses of fluids a day.

"Ideally," she adds, "you want at least half of that to be water."

Some conditions ramp up our water needs.

Obviously temperature is one thing, whether from a seasonal shift or a thermostat redial. The hotter your surroundings, the more you will sweat out your inner water supply and the more fluids you will need to consume. Turning up your own inner temperature through exercise will also increase the need to refuel the fluids.

Experts at the Mayo Clinic suggest that water is fine after short exercise sessions but recommend drinking a sports drink during longer, more intense workouts. Those drinks contain sodium and will reduce your risk of developing hyponatremia, a rare yet possibly life-threatening condition that occurs when you drink too much water.

It happens when the kidneys can't flush out the excess water, making the electrolyte content in the blood diluted. That leads to low sodium levels in the blood. This is very uncommon and mainly seen in endurance athletes, such as marathon runners.

Illness, pregnancy and breast feeding are also factors that will increase our bodies' need for fluids.

And don't forget, those fluids can also be found in food.