No its not, but the body is much more effective when it is hydrated therefore most diets recommend drinking plenty of water while on a diet. Its particuarly important if your doing a lot of exercise, which is the best way to lose weigth.
drinking a glass of water also stops those hunger pangs when you really want to snack - but you should be eating a health, unprocessed diet and excerising to lose weight - good luck
It's not enough on it's own, but it will certainly help, together with good diet and exercise.
"The best way to lose weight is to eat less and do more"
You shoud drink 1 quart of water in the morning, 1 quart in the afternoon, 1 quart in the evening and 1 quart for every 25 pounds overweight you are. Yes, it's a lot of water!