Water is plentiful, inexpensive and (relatively) safe.

So what's my beef with it?

Nothing... if you're drinking it because you're thirsty.

But if you've developed a serious bottled water habit because you've heard it can make you faster, thinner, younger, or healthier... well, on some level you probably know it's not that easy, right?

The truth is, anyone who wants you to believe in these and other supposed health benefits of water is probably just trying to sell you some -- spring water, mountain water, water from Fiji, or plain old tap water in a bottle with a fancy label.

And they're pulling every trick in the book in the name of marketing.

A recent editorial in BMJ looked at the growing number of health claims being splashed into water, and found... well, they're all wet -- starting with the claim that you need eight glasses a day to stay healthy.

You don't.

In the editorial, Dr. Margaret McCartney looked at the research and found no evidence to prove you need to drink like a guppy to stay healthy or even just hydrated. A 2002 study, for example, found "no scientific evidence" for eight glasses a day.

So excess water won't make you healthier... but you're probably thinking that at least it's harmless, right?

Not so fast: Too much water can actually pull essential sodium out of your body, leaving you with a potentially deadly condition called hyponatremia.

It's not as rare as you might think, especially in the sports world. In fact, hundreds of runners in the New York City Marathon end up sick and even hospitalized with hyponatremia every year because they guzzle water from start to finish in the mistaken belief that they're dehydrating with every step.

"There are no reported cases of dehydration causing death in the history of world running," Dr. Lewis G. Maharam, medical director for the New York City Marathon told the New York Times back in 2005. "But there are plenty of cases of people dying of hyponatremia."

And if marathoners don't need all that water, what are the odds you do?

Answer: You don't.

In reality, the only time you need water is when you're thirsty -- and even then, almost any liquid will do: coffee, tea, beer, even the water in food.

And if you want a plain glass of cold water, don't feel obliged to shell out cash for bottled -- most of that stuff is no better than what comes out of your own tap, and some of it might be worse.

Instead, install a reverse-osmosis filter in your home to keep your faucet free of contaminants such as chemical waste and pharmaceuticals.

Then, feel free to drink that water -- but only when you're thirsty.