Tap water is held to a standard of cleanliness much higher than is bottled water.
Tap water is comically cheaper than bottled water.
Let me explain.
The cleanliness of bottled water is regulated by the Food and Drug Administration. The FDA's regulation consists of one sentence: Bottled water suppliers must use an approved source.
"What is an approved source?" might you ask.
[An approved source is] a source of water...that has been inspected and the water sampled, analyzed, and found to be of a safe and sanitary quality according to applicable laws and regulations of state and local government agencies having jurisdiction.That's all well and good, but it leaves most of the decisions on how much effort goes in to the sanitation of the water up to the people whom have the most to gain by spending the least amount of money. So, bottled water companies make the most profit when they spend least money on sanitation.
Tap water, on the other hand, is regulated by the Safe Drinking Water Act by the Environmental Protection Agency, which is far more stringent when it comes to regulating the cleanliness of water than is the FDA. It would take hours and days to explain the extent of the regulations involved in the purification and filtration of tap water, so I won't. Go here for more info: http://www.epa.gov/safewater/sdwa/index.html
Now, as for the financial side of this conversation:
1000 gallons of tap water in Fairfax County, VA costs $1.85.
1000 gallons of the cheapest bottled water you can find (Giant's Acadia brand) costs $1,280.00
1000 gallons of fancy bottled water (Fiji) costs $8,960.00
So if we divide the cost of the bottled water, by the cost of the tap water, we'll find out how many gallons of tap water we could buy with as much money as we spend on bottled.
4.8 million gallons of water. Do you know how many swimming pools you could fill with 4.8 million gallons of water?
7.3 Olympic sized swimming pools is a lot of water.
Think about it the next time you grab a bottle out of the fridge instead of a glass out of the cabinet.