Since most flights are over water or outback Australia what...

Since most flights are over water or outback Australia what would be the point? Would have be the most ineffective way of drugging a nation. Just put it in the water supply.

Vapour trails are what they are called and it is due to water vapour being produced during combustion. Same as what you see out of your car's exhaust on a cold morning. Unless that is a chem trail as well?