If you are feeling thirsty you might already be dehydrated. Drinking water slowly throughout the entire day will allow your body to use natures elixir effectively instead of purging it too quickly.
The recommended intake from the mayo clinic is 9 cups for women (72 oz) and 11 cups for men (88 oz), however, many factors effect hydration so use this tool to find your need; http://nutrition.about.com/library/blwatercalculator.htm
The benefits include support detoxification, loose weight, relieve fatigue, prevent headaches, improve health of skin, look younger, support digestion in preventing constipation. prevent cramps and sprains. (Mayo Clinic 2012)