Did you know that tap water contains random chemicals and is artificially treated?
That's why people may use the tap filter, to counter it.
In a chemistry laboratory experiment, I was doing testing on random liquids to see how conductive they were.. This picture should give you an idea of what I was doing:
The light bulb is only supposed to light up if there is a concentration of ions in the solution, meaning that the chemicals have an electric charge in it.
I put it into a glass of salt water, it lit up very strong.
I put it into a glass of sugar water (soda), it didn't light up.
I put it into a glass of vinegar, it lit up.
I put it into a glass of pure deionized water, it didn't light up.
I put it into a glass of 2% alcohol (booze), it didn't light up.
I put it into a glass of everyday tap water, the light bulb LIT up very dim.
I was surprised.
It is said that generally the chemical contents of tap water in the USA is safe enough to drink by LAW, but I still would not attempt it.. knowing what is inside.
I'm not sure if filters work because I didn't test filtered water.
But anyways, this is why some people may prefer to drink bottled water, because it's been "stated" to be distilled so that it doesn't contain tap water chemicals, theoretically it should not light up if you put the test into bottled water unless the company was lying or you have some treated water in it.
You will never know if the bottled water has conductive electrolytes or not unless you do the testing yourself, it's really the personal choice for anyone to make themselves.
If you want to be truly green by the usage of water, then look for a chance to live next to a river, lake or spring and do all the filtration yourself. That way you don't have to worry about government regulations in tap water, and you don't have to worry about littering bottled water.