Yes and no. Water by itself will not cause you to lose weight. However, keeping yourself hydrated will increase your metabolism, decrease your hunger and help wash fat cells from your body. This combined with a healthy diet and exercise will reduce your weight.
It can help to relieve craving as part of a calorie controlled diet. If you are hungry, drink a glass of water instead of having snack, it will fill you up for a while, and it's calorie free.