If your concern is safety you may be surprised to hear that tap water is tested daily by the FDA. Bottled water is tested weekly. "Under the Safe Drinking Water Act, water suppliers are required to provide an annual report on the quality of your local water and to test tap water daily." (http://food.yahoo.com/blog/beautyeats/22317/tap-vs-bottled-what-should-you-drink).
Even though I saved money by buying bottled water in bulk at Costco. I stopped buying it because I realized how fast I was going through the giant box and how wasteful it really was. Since then I bought a large plastic water container that I fill up and keep in the refrigerator. Water taste cool, clean, and refreshing. My garbage isn't overflowing all the time and I just saved myself $1,500 a year!