I have a couple one-liter Evian bottles, and I always keep them full. I'd say I drink an average of three per day. Sometimes it's only two and sometimes it's five, but I'm going to say three is the average. So 3 liters = about 100 ounces, or about 12.5 eight-ounce glasses. So I picked 11-15. Drinking water is awesome. It's really helped me on my 'diet.' I never used to drink it before. Plus my hair looks better now!