Water is essential to your bird's health. Without an adequate supply, dehydration - and worse - can occur. Many bird owners are discovering the benefits of providing water bottles rather than bowls.
Water bottles are cleaner and more hygienic than water bowls (provided that they are washed daily). Bottles do not allow birds to defecate or dump/dunk food into the water. Both of these unwelcome additions cause unhealthy, infection-inducing bacteria to multiply quickly. Bottles completely remedy this problem. Water bottles are also less likely to spill. (However, if your bird enjoys "showering" under his bottle, the cage bottom may become very wet.)
Many birds learn how to use bottles with little or no hesitation. It's helpful to demonstrate the bottle, then allow your bird to become familiar with it on his own. When transitioning to a bottle, keep the familiar water bowl in the cage, too. Once your bird begins to use the bottle regularly, remove the bowl unless you wish your bird to use it as a bath.
Inspect the water bottle and drinking tube daily to make sure it is not empty or blocked. Some birds enjoy the "game" of emptying it or plugging the tube with a treat. Also, be sure to change the water and wash the bottle daily.