I try to aim for 1.5 litres (53oz) a day, which is the minimum recommended in Britain. However I don't take into account the amount of tea I drink, which is anywhere between 2-5 cups a day (about 8oz for one mug, I read).
Personally, I've found that water really helps me. I drink loads whenever I have a bottle next to me, and I believe I'm less hungry because of it. They say people confuse thirst with hunger and I believe this is genuine because hey, I sure as **** snack a lot less when I have my water