Humans produce between one-fifth and one-third of a gallon (0.75 to 1.5 liters) of saliva every day. However, saliva production mostly takes place while a person is awake. During sleep, saliva production drops to almost nothing. Most of the saliva comes from the glands at the bottom of the mouth, and the rest comes primarily from the parotid glands, near the top back of the mouth.
More facts about saliva:
Human saliva is composed of about 98 percent water. The remainder includes enzymes to break down food, electrolytes, antibacterial compounds and mucus.
It is possible to “milk” salivary glands, and this is often done as a test for those who have malfunctioning salivary glands. Milking the salivary glands allows doctors to observe the flow of saliva and possibly determine what is causing the malfunction.
Saliva is an excellent indicator of personal health and can be used to test for a wide variety of conditions, including human immunodeficiency virus (HIV), osteoporosis and some cancers.