Drink up? Sorting out water truths vs. myths

After years of taking bigger and bigger sips, America is gulping down water: by 2016, bottled water will outsell soft drinks nationwide, and it's already the number one beverage sold in big cities from Los Angeles to Washington, D.C., according to the International Bottled Water Association.

Bottled water sales rose more than 7% in 2014 alone, the group says. Consumer surveys suggest tap water consumption is rising too.

Taking some credit: a campaign called Drink Up, from Partnership for a Healthier America, a non-profit group backed by beverage companies, water filter makers and other interested parties. First Lady Michelle Obama is an honorary chair and launched the effort in 2013. She said, "Drink just one more glass of water a day and you can make a real difference for your health, your energy, and the way you feel."

The latest phase, launching this month, will feature ads online, on billboards, at bus stops, in gyms and elsewhere with the slogan "h2ofcourse" — paired with messages targeted to specific groups. One apparently for Yankees fans: "Dehydration can make you do crazy things. Like root for the Red Sox." One for flyers: "Pressurized cabins suck moisture from your skin. Like thousands of angry little straws."

While the messages are not about health per se, "drinking water is one of the healthiest things you can do," says the partnership's CEO Larry Soler.

Yet the science of water and health is murkier than many consumers might realize. Here's what true and what's myth about several common beliefs:

You should drink eight glasses a day.

Nope. This is a myth, based on the fact that most healthy people do consume about eight cups of fluid a day in their foods and drinks, says Stanley Goldfarb, a professor of medicine at the University of Pennsylvania. "Somehow that got translated into 'drink an extra eight glasses,' " he says.

There's no need to keep count or to get all your fluid from water, says Nancy Clark, a Boston area registered dietitian and sports nutritionist: "Coffee counts, iced tea counts, so do lettuce, soup, oatmeal and fruit."

You should drink water even if you are not thirsty.

Most people, on most days can be guided by thirst alone, Clark says. But in some cases — when you sweat heavily outside on a hot day, for example — it's smart to drink extra, she says.

It's also smart, she says, to pay attention in the bathroom: if you urinate every two to four hours and your urine stays light yellow, you are well-hydrated.

Water helps control your weight.

It probably does — if you drink water instead of drinks with calories, especially sugary drinks such as sodas, fruit drinks and energy drinks, says Barry Popkin, a professor of nutrition at the University of North Carolina-Chapel Hill.

"The general consensus is that liquid calories, particularly when they come from sugar, contribute to weight gain," he says. When people drink sugary drinks, he says, "they don't compensate by cutting back on food. They add calories."

Less clear, and still under study, he says, is whether water drinkers do better than diet soda drinkers.

Water gives you energy.

Not really. Energy comes from calories and water doesn't have any. It is true, though, that dehydration can make you feel sluggish — and that re-hydrating can perk you back up, Clark says.

It improves your complexion.

While serious dehydration will dry your skin, drinking extra water does nothing for it, Goldfarb says. "When you drink a glass of water, it goes all over your body, it goes to the skin on your toes, your muscles and organs… it doesn't go to your face preferentially."

It flushes out toxins.

Your kidneys do that every time you urinate. Drinking more water than you need won't make your kidneys work better, Goldfarb says. You'll excrete the same waste products in more urine.

It's as good as a sports drink for exercisers.

Usually, water is better — because it doesn't have unneeded calories, sugar and salt, Clark says. For people working out hard for an hour or more — think marathon runners, bike racers and football players in long summer practices — a sports drink can provide some extra energy and keep help keep salt and fluid levels in proper balance, she says.

It's better from a bottle.

While bottled water can be convenient and some people prefer the taste to their local tap water, there's no reason to think it's healthier. Tap water is regulated by the Environmental Protection Agency and subject to frequent testing and public reporting of results. Bottled water (which often starts as tap water), is regulated by the Food and Drug Administration, but manufacturers do not have to tell consumers where the water comes from, how it's treated or what contaminants it might contain. And most of the bottles are never recycled, the U.S. Government Accountability Office reported in 2009.