Parakeets are picky about the cleanliness of their water when they want to drink, but they aren't so worried about keeping feathers, waste and seeds out of it when they're playing, bathing or eating. Unclean water's just one reason why your parakeet might not drink, so for starters, make sure the water's always fresh.
Your parakeet's water is quickly tainted by droppings, seed and bacteria. Once that occurs, he may be reluctant to drink it. His water dish should be cleaned and refilled with fresh water no less frequently than daily -- but more often is probably the best way to keep the water fresh for all but the most fastidious birds. You may change water many times in a day if you have especially messy birds or birds with refined tastes. If the water is clean and fresh and he still isn't drinking, add a few drops of honey to entice him. You can also replace the water with an oral electrolyte solution or a diluted sports drink. Offer bottled drinking or spring water so that he isn't absorbing chlorine or heavy metals found in tap water. He may also prefer the taste of spring water over tap water. If your bird stops drinking completely or seems ill, contact your veterinarian immediately.