[narag]

A fast object compress the air in front of it reducing the amount of water that can be solved into it, so the excess of water condenses.

It's very visible in planes about to break the sound barrier. Look for Youtube videos. The cones are spectacular, but also notice how a trail is sometimes visible originating from the tips of the wings.

So you don't need to inject the water, but to extract it from the air compressing it. Anyway, I'd bet the meteor trails consist of vaporized matter from the meteor itself.

Edit: see this one at 0:20:

http://www.youtube.com/watch?v=gw9MjutMhLs

[lutorm]

It's true you can get water condensation features from local pressure minima like in wingtip vortices. However, they are transient, because as soon as the air returns to ambient pressure the condensation goes away.