A general rule that many backpackers (including me) follow is to carry 1 liter of water for every 2 hours of walking. Adults usually need 2 cups of water per hour of walking. Children usually need 1 to 2 cups of walking per hour. However, you may need more or less, depending on whether you can filter water along the way, weather conditions, and personal thirst.
It's always best to be careful and carry more water than you think you'll need for the hike. How much water is enough to take on a camping trip? A good rule of thumb is to bring two gallons of water, or about seven and a half liters, per person per day of camping. Carrying this amount of water means you must have enough drinking water, water for cooking, cleaning and personal hygiene. To summarize the question of how much water you should bring when camping, as an adult, you need about 64 ounces of water on an average day.