In an entire human lifetime, the average person produces around 100,000 gallons of saliva. Just to give you some sense of volume, picture how much an an average American family uses in water -- indoors and outdoors -- over the course of a year. Looking at it another way, you could fill about three and a third in-ground 20-by-40 foot rectangular pools . . . with spit.
That's definitely more than a "bucket of spit" (which is an idiom that means "not worth anything)." As people age, their salivary secretions also decrease making them more susceptible to dental diseases, so your saliva is worth a lot more than you think.
Saliva is mostly made up of water, but it contains important enzymes that your body needs to digest foods and keep your teeth strong.
In addition to simply aging, many medications can also decrease salivary flow, leading to an increase in tooth decay. If you suffer from dry mouth, let your doctor know. There are steps you can take to reduce your risks. If you don't, you could find yourself "spitting into the wind" -- especially if you are trying to cut down on cavities.