I think you would drown first. Wait, would you be able to float in spit? Depends on how salty/contaminated with gunk it is. Assuming you don’t drown, I don’t think you would dissolve in spit, as your skin is pretty tough. If you stick a chicken leg in your mouth for a bit, sure it would get gooey and yucky, but it wouldn’t just dissolve. That’s what your stomach acid is for. I think saliva softens up the food, but not dissolve it, but I didn’t choose Biology, so what do I know.

There’s also a very high likelihood that you get really sick though, who knows what’s in that spit? Not to the mention it’s probably from hundreds, if not thousands people given that there’s enough to fill an entire pool.