Bottled water is not necessarily purer or safer than tap water;
Bottled water costs hundreds to thousands of times more than tap water, and
   tens to hundreds of times more than home-treated water;
Bottled water has often been demonstrated in blinded tests to taste the same
   as tap water;
Bottled water can have no magical properties to cure disease, help you hydrate
   any better, give you more energy, or lose weight faster than tap or filtered water;
Bottled water wastes resources and pollutes the earth and atmosphere at every
   stage of its production, distribution, and disposal.
Are there any benefits to purchasing bottled water?  Are there better, more
   affordable strategies to satisfy your thirst on the road?

There are times and places where the immediate availability of safe water is critical, like in the aftermath of a disaster where normal water distribution is interrupted &/or the local water is polluted.  Bottled water can help tremendously in those situations.

When traveling out of town the water quality/safety may be unknown (or known to be bad).  That would be another instance where purchasing bottled water would make sense.  

In the absence of a disaster or travel, however, the main (and arguably the only) benefit to bottled water is convenience - you can take bottled water with you wherever you go or purchase it when you get "there" and be reasonably assured of drinking safe, good tasting water.

Of course it has always been possible to take water with you - back when I was a kid you simply filled a canteen or thermos from the faucet and went on your way.  Today there are a wide variety of reusable water containers in plastic, metal, glass and ceramic.  Plastic and metal are most commonly used for individual-use portable containers and glass and ceramic are mostly limited to bulk water storage.

Alternatives to purchased bottled water
Drink the local tap water - In most cities in the US and other developed
    countries the local tap water is safe.
    Check if traveling, and if there is any question about the water quality use a
    portable water treatment device or buy bottled water.
Fill your own reusable bottle!
    Filling your own reusable bottles and effectively cleaning them between uses
    does take some time and uses resources (water, soap, energy to heat the
    water, and "elbow grease").  Some of the "convenience factor" of pre-packaged
    of purchased bottled water.

With a moderate initial expenditure and attention to cleaning the container,     bottling your own tap water will cost well under a cent per gallon. If you have concerns about using tap water to drink and fill your reusable      water containers, you can economically treat your water with any of      the legitimate methods described on this page that fit your needs      and fill a 16oz water container for $0.01 or less to around $0.04.

Concerns have been raised about the safety of some types of plastic containers. 
National Geographic Green Guide - Plastic Containers: Introduction
Plastic Containers: Health Issues
Plastic Containers: Solutions
Safer plastics - #2HDPE, #4LDPE, and #5PP
When choosing plastic containers, even those you'll use over and over again, choose those that are accepted for recycling in your area. Although #1 PETE is one of the most commonly recycled types, there are no containers designed for re-use made from it, and one should never re-use single-use #1 plastic bottles because their design doesn't lend itself to proper cleaning and the bottles can harbor bacterial growth. There are, however, a number of reusable containers made from another commonly recycled plastic, #2 HDPE. Number #4 LDPE and #5PP plastics, although not as widely recycled, are also good choices since, as with #2, most research has not shown leaching of any carcinogens or endocrine disruptors.

Basic Plasitc Info and Tips and the Smart Plastics Guide
Avoid polycarbonate (#7) baby bottles and sippy cups.  For baby bottles, try and use glass (e.g., Evenflo), polyethylene (e.g., Evenflo, Medela, Playtex) or polypropylene (e.g., Gerber, Medela) instead.  Sippy cups made of stainless steel (e.g., Kleen Kanteen), or of polypropylene or polyethylene (e.g., Avent, Evenflo, First Years, Gerber, Playtex) are safer.  Be sure to check the bottle or cup to be sure of the type of plastic it contains.  As for baby bottle nipples, try and use silicone which does not leach the carcinogenic nitrosamines that can be found in latex.

Bottled Water Backlash
None of the following plastics have been shown to leach carcinogens or endocrine disruptors.
#2 HDPE (high-density polyethylene) is durable and widely recyclable.
#4 LDPE (low-density polyethylene) is used in some food wraps and sandwich bags.
#5 PP (polypropylene) is popular in reusable containers, though not frequently recycled.
For an alternative to plastic, try the Thermos Stainless Steel Beverage Bottle #2550. With a stainless-steel exterior and interior, it keeps beverages cold or soups, coffee and tea hot 10 times longer than plastic bottles, or try Sigg 's .6-liter Oval Traveler Reusable Bottle in stainless steel. {other brands of metal containers you can look up on the web include Klean Kanteen (stainless steel), Sigg (ceramic-lined aluminum)
What You Can Do
Avoid leaving water in any plastic bottle in the heat. {this would include purchased bottled water}
Hand wash reusable bottles gently.
Don't reuse PET bottles - particularly baby bottles.
Fill reusable bottles with your own tap water, filtered if necessary.

Is reusing water bottles safe?  A little research has turned up two opinion groups:
the refillers: The refillers say that washing and re-using water bottles is safe, particularly if they
   are washed regularly with hot, soapy water.
the non-refillers (represented, in particular, by the International Bottled Water Association, an
   organization that represents the interest of companies that sell bottled water): Those in the
   non-refilling camp state that only bottles specifically made to be reused should be refilled. For
   starters, they say that all kinds of bacteria can thrive in made-to-be-disposed bottles, even
   after washing

Message in a Bottle-1: Americans spent more money last year on bottled water than on ipods or movie tickets: $15 Billion. A journey into the economics--and psychology--of an unlikely business boom. And what it says about our culture of indulgence.
from Fastcompany.com, July/August 2007
...Bottled water is often simply an indulgence, and despite the stories we tell ourselves, it is not a benign indulgence. We're moving 1 billion bottles of water around a week in ships, trains, and trucks in the United States alone. That's a weekly convoy equivalent to 37,800 18-wheelers delivering water. (Water weighs 8 1/3 pounds a gallon. It's so heavy you can't fill an 18-wheeler with bottled water--you have to leave empty space.)...
...Bottled water is not a sin. But it is a choice...
...Once you understand the resources mustered to deliver the bottle of water, it's reasonable to ask as you reach for the next bottle, not just "Does the value to me equal the 99 cents I'm about to spend?" but "Does the value equal the impact I'm about to leave behind?"

Message in a Bottle-2: Despite the Hype, Bottled Water is Neither CLEANER nor GREENER Than Tap Water. from emagazine.com September/October 2003
...A 2001 World Wildlife Fund (WWF) study confirmed the widespread belief that consumers associate bottled water with social status and healthy living. Their perceptions trump their objectivity, because even some people who claim to have switched to bottled water “for the taste” can’t tell the difference: When Good Morning America conducted a taste test of its studio audience, New York City tap water was chosen as the heavy favorite over the oxygenated water 02, Poland Spring and Evian...

I am checking on the links below which currently do not work.
Where Gas Is Cheaper than Water
May. 25, 2006
Bottled Water Biz - Americans spend billions on bottled water, but it's really no better than tap. May. 11, 2006
Selling the Air We Breathe - Some marketers think bottled oxygen industry could be as big as bottled water. Apr. 21, 2006
Good Humor: Bottled Water
Nov. 11, 2005

Inside the Bottle is a Polaris Institute project designed to stimulate citizen awareness about the bottled water industry. This site has begun to map the bottle water locations of the industry's Big 4 corporate players. Citizens are invited to contribute to this map by investigating and reporting how the industry operates within your community.