Water increases calorie burning by diluting the blood going to the liver (portal circulation) and by turning on the sympathetic nervous system (the body's fight-or-flight system). The cells have very sensitive methods for regulating fluids in blood, cells and the space between cells. Water intake activates this system, which increases caloric expenditure. Drinking extra water has little effect on weight control and could be dangerous...just like anything. You must find the right balance that works for you and how water plays into your everyday activities. The 20 calories you expend processing the water is equivalent to jogging for two minutes. But again...don't forget, excessive water intake can cause hyponatremia (water intoxication), which can be deadly.
So remember to stay hydrated each and every day...do not go overboard on your water intake especially if you are not active. Water has and will always be vital to your survival. It participates in almost all the chemical reactions in your body, it helps cool you, and moves vital fuels and hormones to your muscles and tissues. Just be aware that just like anything else...there have been known cases of people drinking too much water and dying from these decisions. BALANCE IS THE KEY TO EVERYTHING IN THIS LIFE! So be ACTIVE and DRINK YOUR WATER!!
Journal Clinical Endocrinolgy Metabolism, 92: 3334-3337, 2007)