LordKAT is bang on the money here, but I just thought I'd add that it's a good idea to keep the water chilled (or drink it with lots of ice). I read some research several years ago where they found that cold water will slow down your stomach - almost paralysing it for short periods - so you will feel less hungry because your stomach is 'stunned' by the cold. I drink about two litres a day, which I keep in separate 1-litre, pre-chilled bottles (so it's always cold when I drink it),
Also, most body fat comes from excess carbs, not excess fat in your diet. Refined sugar is especially bad, so try to not have any at all. Use low-calorie sweeteners if you really need some sweetness (but avoid those containing sucralose, because recent research has found that your body metabolises those into fat in the same way as sugar) but just try to go without if you can. Above all else, avoid carbonated drinks. Popular brands of cola contain around 8 teaspoons of sugar in each glass... so they're really bad for you if you want to lose weight.
I've cut out many of the carbs from my diet: I have a hit of them at breakfast in my high-fibre, high-fruit cereal, but then I'll have chicken breast with a ton of salad at lunch, followed by meat of some sort and either salad or low-calorie veg (broccoli, cabbage, carrots etc. - as much as I can pile on my plate) for dinner. I avoid sweets/candy like the plague: I just picture them going straight to my hips and that's enough to turn me off the idea. But I'm not out to punish myself, so like Jack_M I give myself one 'off' day in the week, when I can eat whatever I like. It's usually Sunday, but if I have a major craving for a chocolate bar on a Wednesday I'll make that my 'off' day for the week and get right back on the wagon on Thursday.
The biggest cause of my hunger is a lack of sufficient protein, which is why I try to fill up with hi-protein, low-carb foods like broccoli.