Plastic bottles can also leach chemicals, such as BPA (bisphenol A) into your water. Plastic containers that have the number 7 recycling code on them usually contain BPA. Recent studies have shown BPA to be toxic to animals, and potentially to humans.
One way to keep the environmental impact down, as well as to protect yourself from exposure to toxic chemicals, would be to invest in a BPA free water bottle. If you prefer plastic, Camelbak makes a great BPA free water bottle. They also recently came out with a stainless steel water bottle. Another well known maker of stainless steel bottles is Klean Kanteen. Many people also like the Sigg bottles, although these are aluminum, which has been shown to have its own issues to consider (more about this later). The Sigg bottles do have a liner that is supposed to protect you from the aluminum. Whichever bottle you choose to use, please consider purchasing a reusable bottle... both for your health and the environment's sake.
Sources:
http://webecoist.com/2008/11/26/amazing-frightening-green-facts-environmental-statistics/
http://www.chicagotribune.com/features/lifestyle/green/stv-green-storygallery-tipsandfacts,0,7677451.storygallery
http://en.wikipedia.org/wiki/Bisphenol_A
