There are many causes of a white tongue ranging from benign to potentially serious. It is important to see your dentist
every six months or sooner if you are concerned. A healthy tongue is pink, painless, and covered with tiny bumps called papillae. These can become irritated and appear white in color. Waking up with a a white tongue in the morning might just be due to poor hygiene. Make sure to brush your teeth and tongue twice a day. Another common reason for a white tongue in the morning is if you have been breathing through your mouth instead of your nose the night before which will dry out your mouth. This is commonly due to allergies or a cold. Dehydration, smoking, and medications that cause dry mouth can also cause a white tongue. If your symptoms resolve after getting a drink in the morning it is likely due to one of the above mentioned causes of dry mouth.
Another cause of white tongue is thrush, which is a yeast infection in the mouth and requires treatment. Other less likely conditions which cause a white tongue are leukoplakia which is a potential precursor to cancer and oral lichen planus which causes a lacy white pattern on your tongue and its cause is often unknown.
As it is not possible to diagnose your condition without an exam please see your dentist or primary care provider.