Drinking water is important if you're trying to lose weight, some studies have shown that thirst and hunger sensations are triggered together. If there is a slight dehydration the thirst mechanism may be mistaken for hunger and one may eat when the body is actually craving fluid. As most food contains some water, if one doesn't drink much they may be subconsciously driven to eat more to gain the necessary water supply however, you also gain the undesired effects of increased calorie consumption. Drinking more water can help to prevent overeating and benefit weight loss.
For the average person, experts suggest getting at least one and a half litres of water daily or eight glasses. If you are on a diet to lose weight it is more important to consume more and keep drinking water throughout the day, unless you have any medical condition that doesn't allow much water intake.
A good guide for daily intake is to drink 30 millilitres of water for every Kilogram of body weight. A 90 Kilogram person should be drinking around 3 litres (12.5 cups) of water in order the gain the benefits of increased energy and metabolism.