This is not for you. Water Water is necessary for life. Without water, you die. For cyclists or anyone who exercises outside, this is very important. First Aid course or any Boy Scout or Girl Scout safety course will cover the essentials.
Water means just that.
Other drinks may contain sugar or caffeine or both. Your body needs food, which it converts to sugars to fuel your muscles. This readily available fuel is stored in your liver and muscles as glycogen, and is available to be used now, to run, walk or ride your bike. After about 2 hours of exertion, this stored supply of energy runs out and your body begins to convert stored fat into energy. This process is more complicated than simply utilizing sugars, and is much less efficient.