MADISON, Wis.?The human body is composed of about 70 percent water. Take that as a hint.

Water is at the top of the list of things you should be drinking plenty of, says Dr. Kristina Penniston, a clinical nutritionist with the University of Wisconsin School of Medicine and Public Health (SMPH).

Penniston, who works primarily with kidney specialists, says what you choose to drink, and in what quantity, has a huge impact on the health of your kidneys and other parts of your body. Every day, the average American guzzles several quarts of liquid --everything from good old H20 to drinks like coffee, soda, juice and alcohol.

Water is best, but you don't necessarily have to heed the old saw that suggests you drink a full eight glasses a day.

"Our need for fluids varies so much, and there's really no one-size-fits-all amount," says Penniston. "Everything depends on what you're doing?are you sweating during physical activity or are you sitting at a desk being sedentary?"

If you're looking to avoid kidney stones?and given the pain they can cause, you should be?both lemonade and orange juice both contain a citrate that helps prevent the buildup of calcium oxylate, the substance that forms kidney stones.

That's a good thing. But there's also a drawback: both beverages are laden with sugar and calories.

"We don't drink eight ounces of pure lemon juice, which is what actually provides the protection," says Penniston. "We dilute it with water and sugar, and that changes the equation of how healthy it is fairly significantly."

Cranberry juice has its share of sugar, too, but some recent research suggests it also has something else: a substance that may inhibit the strains of e.coli bacteria that can cause painful urinary-tract infections.

"We know that you can show in a test tube that the infectious bacteria are kept in check by cranberry juice," says Dr. Dr. Sarah McAchran, an urologist and assistant professor of urology at UW. "The question is, when you drink the juice, does the protective element excrete into the urine and the urinary tract?"

Grapefruit juice is packed with vitamins and minerals. But if you're on certain types of antidepressants, or using statins to control cholesterol, you need to avoid it, because it interferes with the body's ability to metabolize the drugs. In some cases, the interaction speeds up the body's response to certain drugs, creating a dangerous and life-threatening situation.

Then there's soda, the favorite beverage of many--if not most-- Americans. In fact, the United States is responsible for more than a third of the world's total soda consumption every year. Penniston suggests we should choose another option?or at least cut way back.

"I would really ask people to wake up to the fact that the amounts of high-fructose corn syrup found in most types of sodas are associated with all sorts of troublesome health issues, from obesity and kidney stones to gout and insulin resistance," she says.

Diet sodas don't lead to obesity, but they aren't necessarily much better. A 2009 Brigham and Women's Hospital study suggested that women who consume more than two diet sodas a day may be doubling their risk of kidney-function decline.

Vegetable juice drinks seem like a no-brainer?after all, aren't all those great vitamins in things like tomato juice cocktails wonderful for us? Well, yes. But the huge amounts of sodium that accompany some of them aren't.

"The kidneys actually mirror the heart in several ways," says Dr. Stephen Nakada, head of the division of urology at UW Hospital and Clinics. "And that includes the fact that too much sodium isn't good for either of them. High levels of sodium contribute to kidney stones, and are a risk factor for high blood pressure and heart attacks."

Sports drinks are also loaded with sodium, which makes them an odd choice for those who drink them while sitting in their cubicles rather than after a 10K run.

"It's good to remember that these drinks were formulated for elite athletes who need to replace fluids lost to sweat," notes Penniston. "The rest of us probably shouldn't drink them unless we need them." Opting for the low-sugar and low-sodium versions of these drinks is another possibility.

The bigger issue with many of these drinks, says Dr. Nakada, is actually the size of the bottles. In recent years, both soda and sports-drink bottles seem to have been put on some kind of steroid regimen?20 and 24-ounces bottles have edged out 12 and 16-ounce servings. Some companies have also begun to offer smaller-size serving options, but big bottles still dominate the shelves.

"If you're smart, you're staying away from large drinks," says Dr. Nakada. "Whatever drink you're talking about, the bottom line is you should try to avoid excesses, and simplification is best."

Dr. Penniston agrees. "The key to all of this is that your beverage intake should be diverse, and it should center on moderation. You don't want to have too much of any type of drink."

-30-