Admittedly I've been very skeptical about so-called chemtrails. But I've also cleaned the residue from jet exhaust off the waterline tiles of my pool, which I had to do at least once a day. When I had a pool that wasn't directly below flight paths, I would only have to scrub the waterline tiles once or twice a year.

I don't know about the chemistry, but I do know about the physics (thermodynamics). Water vapor wouldn't disperse like that, much less visibly as it would reach thermal equilibrium with the surrounding moisture in the air.