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How much water do we really need?

Elizabeth Cohen gets to the bottom of the eight glasses per day myth.  

You've heard it for years -- drink at least eight glasses of water a day. But now some scientists say that may be an urban myth. CNN Medical Correspondent Elizabeth Cohen joined CNN's Paula Zahn to discuss the issue.

PAULA ZAHN: I have to tell you, Elizabeth -- good morning -- I am so ticked about this. I'm one of those people that's become accustomed to walking around with the big plastic bottle of water, and they laugh at me every morning because I try to ...

ELIZABETH COHEN: You're one of those nerds, is that it?

ZAHN: ... I try to get through six glasses right here during the "American Morning" show. So I've been living in a state of flotation for many years here, and now you say I didn't need to do this. What's going on?

COHEN: Well, actually, before I tell you that, Paula, I have to ask you, do you sweat a lot during the show?

ZAHN: Never...

COHEN: Never, then you don't need all that much water.

ZAHN: ... because they keep the air conditioning here at like 60 degrees to make sure everybody's alert and thinking well.

COHEN: Right, exactly. Yes, it works, too, doesn't it?

ZAHN: Yes, it does.

COHEN: Well, if you're not sweating a lot during your show, then you probably don't need quite as much water as you think you do.

This eight eight-ounce glasses a day it turns out, after talking to the USDA, the National Academy of Sciences, the National Institutes of Health, people at various universities, they say, you know what, this appears to be kind of a myth. We can't find a single study that says that that's what people ought to do.

So I'm sitting next to a myth. Let's show the myth that I'm sitting next to. This is eight ounces -- eight eight-ounce glasses of water. This is, theoretically, according to the myth, what you're supposed to be drinking. You can also look at it this way, that you're supposed to be drinking these two containers of water. All those people who are, you know, being, I guess, nerds like you, Paula, and walking around with those big bottles of water.

I'm just kidding: You're not a nerd at all, but people are now saying, gosh, is this true?

And what we've heard is that this doesn't appear to be true and also that there's nothing magical about water. Of course, you need to keep yourself hydrated. We're human beings. We need to have some form of hydration -- doesn't have to be water.

Let's look at the water content of some other food and beverages here. For example, milk -- 84 percent water. You could get your water there. Watermelon, 85 percent water -- you could get your water there. Other fruits also have lots of water. Diet Coke, 99 percent water -- you could get your water there.

Now I can hear you thinking, well, gee, you know Diet Coke, that has caffeine in it, that can't be good. We've all heard that caffeine is dehydrating. However, we've talked to a couple of experts who point to studies that say, you know what, when we look at it, people get just as hydrated from caffeinated beverages as they do from decaffeinated beverages. So of course you don't want to drink just caffeinated beverages all day, but if you have a cup of coffee in the morning and a cup of tea in the afternoon, you can count that as some of your water -- some of your water intake.

So the bottom line here is that the eight eight-ounce glasses a day appears to be conventional wisdom. We don't really know what the real answer is, but you can sort of use common sense. And just know that you need to keep yourself hydrated. You start to get a headache, you start to get thirsty, start to get a dry mouth, means you're not drinking enough -- Paula.

ZAHN: Don't you just love the fact that we'll never know how much we're really supposed to drink?

COHEN: Well, we may know in March, because, actually, the National Academy of Sciences has put together a panel of experts to do nothing but look at how much water do we need. And hopefully, in March, they should have the answer. And so in the meantime, you just have to sort of use common sense.

ZAHN: And in the meantime, I will just have to get rid of my addiction, won't I?

COHEN: No, water is great.

ZAHN: My constant traveling companion.

COHEN: Water is great. There is no reason not to drink water. I mean drink, drink, drink. Go to town on water. It's not going, obviously, to do anything for you; it can only do good. It's just that that eight glasses that we've all had stuck in our head -- I know I sometimes spend a day going, Let's see, I had a glass there, a glass here, does that add up to eight? You know you don't need to be that neurotic.




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