1st: i am a newbie when it comes to optics and hardly know anything abt it but recently i am trying to learn more abt it. . and i have a question:

what will happen if we have 1 parabolic lens (1 side flat) and we place it on a flat mirror. will it act like a parabolic mirror ?

for example:
we have a circular flat mirror, and we pour water on it and start rotating the mirror at slow RPM like mercury telescope in canada. so what will happen in that case ? parabloic shaped water on flat mirror ?
will it act like perfect parabolic mirror or just low quality stuff ? anyone with any thoughts abt it ?

thanks in advance.