1) Tap water is FREE. And perfectly safe to drink, depending on where you live. Plastic water bottles can be super pricey. Even at $1 a day (I rarely see them sold for that cheap), a glass water bottle can save you over $300 a year.
2) Glass is much safer to drink from. I don't know about you, but I'm personally not going to risk drinking from a plastic water bottle that may or may not include BPA, that can mimic estrogen, which may have detrimental effects, including cancer of the brain, breast, and prostate, on the female reproductive system and the immune system in adults. (http://www.npr.org/2011/03/02/134196209/study-most-plastics-leach-hormone-like-chemicals)
3) Adorable, endless options! I have three glass water bottles that I rotate; two love bottles (http://www.lovebottle.net/) and one that has an adorable knit koozie. Check them out: http://www.freakerusa.com/collections/all. (I have the Ralphie) Don't they make you want to run out and buy a glass water bottle?! How much more appealing are they than plastic water bottles? I get complimented on mine often, and who doesn't love compliments? I sure do.
4) LESS WASTE! Plastic water bottles produce millions of tons of waste each year. Think of how easy that would be to avoid.
5) Think about what a pain in the ass it is to get a case of water bottles form the grocery store, into your car, into your house. For me, getting a case of water bottles into my dorm room was something I dreaded all week, they are heavy as hell and take up a ton of space in those small rooms. The solution: a glass water bottle! Takes up a fraction of the space, and you can fill it up as you please.
To me, buying bottles of water is like buying bottles of air. What sense does it make to pay ridiculous prices for something that is freely available to us? This is what I mean by think for yourself. If something seems off, it's because it probably is. It really isn't that complicated.
So.. can you think of any good reason to keep drinking from plastic water bottles? Take control of your health, your funds, your time and energy, and get yourself a beautiful new glass water bottle!