Water is essential for life. There wouldn't be the proper functioning of body processes without it. An inadequate water intake relative to recommendation contributes to the decline in physical capacity and adversely effects on cognitive function and mood. On the other hand, an adequate water intake helps maintain the balance between total energy intake and daily energy expenditure and determines the correct rate of fat oxidation. This might be useful and commonly used in weight reduction and thus might favorably affect on body composition in overweight and obese people by increasing the total body water and lean muscle mass and might contribute to a decrease in body fat. Research results indicate clearly that drinking water instead of caloric beverages might be an effective way to reduce daily total energy consumption and in this way might may contribute to the reduction of weight, body circumferences and body fat.