Most health resources suggest you should drink eight 8 ounce glasses of water a day, or 64 ounces. Assuming you’re buying water in 12-ounce bottles, that’s 5.3 bottles of water a day. If a case of 12 water bottles costs $6 or $0.50 a bottle. One year of drinking bottled water would cost $965.25. The cost of a water filter is a one-time cost of between $400 and $500.