Don't worry - there's no need to down two litres of water at once. The best way to keep hydrated is to keep topping up throughout the day. A lot of your water intake comes from fresh fruit, vegetables, juices, and even tea. If you're a coffee fan, remember it's a diuretic and follow each cup with a glass of water to minimise dehydration. Make sure you take your water bottle with you to the gym, and if you go out drinking, try to switch between alcohol and water throughout the night. If you forget (nobody's perfect), at least have a large glass of water before bed.