As you yourself said, most of saliva is water. That should give you the information you need.
This question boils down to how water damages electronics and what you can do about it if you get water on electronics.
Water does two things:
If the water comes in contact with a piece of metal (a trace on the board, a pin, anything that's electrified) while it's powered on, the water dramatically changes the electrical characteristics of the circuit. Because water conducts electricity fairly well, the other risk is that water can effectively bridge the gap between two circuits that are ordinarily separate on one of the components, causing it to short out. This can cause components to be "fried", which means that due to the altered resistance properties of the new circuit of "circuit #1 plus water plus circuit #2", a component received far more current than it was designed to handle, which caused it to fail.
If the water comes in contact with circuitry while it's powered off (not in a "warm" state but completely off), there's the possibility that it will cause corrosion. Now, according to this answer on EE.SE, it's not so much the water itself that causes corrosion, but the impurities in it (other chemicals that are more corrosive than water). Corrosion is effectively adding oxygen (usually O2 or O3) to molecules that don't need to have an oxygen bond on them; the typical example of iron is that "rust" -- corroded iron -- is iron oxide.
Anything that's a strong corroding agent that's mixed with the water will do this, moreso than the water itself. So, while it's safe to get perfectly pure water on powered-down electronics, it's not safe to use tap water, or even purified drinking water, because there are still a lot of mineral salts left in the water that are corrosive to the metals used in electronics.
If you're worried about accidentally getting water -- er, saliva, but same thing -- on your electronics, then obviously using a mask is a good solution.
And if you do get water on your equipment, the rice method doesn't work. Here is a video explaining why; Warning: strong language in video.