All water is not created equal.  Water from the tap as well as bottled water will vary in taste, nutrients, and even contaminants.  To confuse things even further two separate agencies regulate water consumption. The EPA sets standards for tap water derived from public sources.  As the official policing arm of all food and drug products, the FDA sets standards for bottled water.

Water Source

All drinking water comes from similar sources such as rivers, springs, and natural underground sources.  Though water varies greatly depending on geographical location, public facilities generally treat water in some manner before it is ready for human consumption.

Public-Source Tap Water.  If your tap water comes from a public water supplier, you can find out exactly where the water comes from, how it is treated, and contaminants found in the water in an annual water quality report required by the EPA.  Your local town government can direct you to the proper contact source.

Well Water.  Just as with public-source tap water, well water can vary greatly depending on geographical location.  The EPA recommends that private well water be tested regularly.  The EPA does not regulate well water but they do offer information private drinking wells in your region. http://www.epa.gov/safewater/privatewells/whereyoulive.html

Bottled Water. It may surprise you to know that the clear, cool stream you imagine as the source for your favorite bottled water may in fact be a public water source in an urban area.  The best way to find out the source of your bottled water and how it is treated is to read the label before you buy and/or contact the manufacturer directly.

Water Quality

Bottled water generally has the taste edge over tap because in most cases bottlers have more options of disinfection methods.  Public -source tap water disinfection methods generally use chlorine or chloramine because they have the ability to maintain disinfection while traveling from the source.  These treatments also often leave an aftertaste.  Bottlers of water on the other hand, have the option of using alternate technologies like ozone and ultra violet light, as they do not have to worry about maintaining disinfection once the water has been sealed in a bottle.