Here's an article I found about why drinking water helps, so hope it helps you out.
"Drinking water is an essential aid to the weight loss process. Drinking water to lose weight works by flushing your system of built-up toxins and curving hunger pangs. Your body requires eight, 8-ounce glasses of clean, pure drinking water each day. Drinking water facilitates weight loss and helps you stay healthy and regular, even when you are on a diet. If your drinking water does not taste good to you, add a slice of lemon to each glassful. Remember that drinking eight 8-ounce glasses of drinking water each day is as important to weight maintenance as it is to weight loss. Don't make the mistake of thinking that by cutting back on water intake, you will prevent water retention. The opposite effect will take place. By drinking more water your kidneys will be stimulated, helping to reduce water retention; and, in the process, your body will burn some more calories. Drinking water to lose weight is the only way beverages will aid in the weight loss process. In other words, drinking diet drinks will not aid in the weight loss process. Not only do diet drinks contain caffeine and calories, their artificial sweetness can turn on your appetite without satisfying it, possibly leading you to overeat at other times."
You can drink other drinks as well on top of your 2L of water.
I use to easily drink 2L or more of Pepsi Max a day and no water and lots of bad food. But i've found now, drinking at least 2L of water and the right food, I dont' tend ot feel the need to eat bad food, I'm fuller for most times during the day and if I get a craving, I guzzle down a big glass of water which fills me up and I feel full, I forget about the bad food. And I know only drink about a glass of Pepsi Max a day, sometimes 2 but not as much as I use to drink.
Hope this helps you out!