Most water bottles hold around 20 ounces, or just under 2.5 cups. This is a convenient size for carrying around with you and staying hydrated throughout the day. Some water bottles are even larger, holding up to 3 or 4 cups of water. Whether you're looking for a small water bottle to take with you on the go, or a large one to keep you hydrated at home or at the office, there's a water bottle out there that's perfect for you.