I don't use tap water on my plants, since mine has iodine added and some plants don't like it (it tastes nasty, too), and a lot of bottled water has all the good stuff filtered out of it. If I could suggest a third option: Rain water. I have never had a plant dislike good old fashioned natural rain water saved in a barrel under my gutters.

Good luck with your experiment.

-Nick

It really depends on a lot of factors. First you have to define bottled water and tap water. There are a lot of different sources of the generic term bottled water. Some bottled waters are actually just tap water that a city has bottled, while others are spring water, or water that has been purified in some manner. Others may have been created from a combination of sources, such as tap water that's been purified. The tap water depends on if you're in a city or on a well, how hard or soft the water is in the area, how old the pipes are and what material they're composed of, and if the city adds chlorine or other chemicals to the water. If you want to do the project correctly you'll have to address these factors. It may be better to narrow the scope to something simpler like is spring water from X spring better than tap water from Y city.

I once worked in a laboratory where we needed to know what was in our water. I ran some sophisticated test and found the same stuff in bottled "distilled" water from the store as in tap water. I called the company and they just volunteered that their "distilled" water came from the tap. BTW, we eventually bought our water from a medical supply company.

You might find ideas about different sorts of water at Wikipedia.

The Wikipedia entry on "bottled water" is quite readable.

Here is a link that might be useful: Wikipedia entry on bottled water.

Chlorine and flouride are harmful to plants, but generally not fatal. Most plants deal with it just fine, but some like spider plants will have duller colors and be more susceptible to tip burn.

For sensitive plants rainwater is the best option.

If you can get some pH paper, you can test the pH of tap water, bottled water, and your soil. Houseplants do best with a pH of about 6, but potting soil can be pretty acid, with maybe a pH of 4. So, depending on the pH of your water, you can actually change the pH of the soil.

It could be helpful for you to contact your city and ask for a list of the mineral and chemical content of the water. What is in the water will affect the growth of the plants.

I prefer to use rain water and, for my plants that I start during the winter, melted snow. City water has such additives as chlorine and fluorides, neither of which is good for plants. And some well water has an unfavorable mix of dissolved substances. For example, Boron is a necessary trace element for plants, but a little too much and it can become toxic.

MM

You should do your own project

The best is rain water is best when growing plants due to
it nature brought state. Tap water and bottled water has been filtered or had minerals and that crap added to it, some of which could be bad for plants. Remember rain water is best, but before you go to the extreme to figure this out, find a book that talk about the flower and (or) veggie you are planting.:)