Water is very important, and in this case, helpful in your diet. By no means deny yourself from it.
With water, you can make yourself eat less by drining a full glass an 30 minutes to an hour before meal and then have your meal. By doing so, you will feel full sooner.
Another thing you can do, unrelated to water is to put your food in a smaller plate. i've read and was told that we're conditioned to finish whatever is on our plate. After all, whart are we told by our parents to do? "Finish your food".
Major restaurants know this so they provide their customers large plates so that they'll consume more food, we'll finish whats on it thinking that the amount is adequate, when really, its a lot. So, use a smaller plate 6 inches in diameter or smaller.
Last tip, is to eat small snacks ... frequenlty. Not chocolates or any sweats but nuts and fruits. By doing that, you'll raise your metabolism. Not only that, you'll eat less in meals.