Hey guys, would it be a good idea to use convex/parabolic mirrors as a way to heat water? Or would you rather go with the generic copper piping idea?

Both systems are in use.

The parabolic mirror approach has two aspects that restrict it to limited use.
First the mirrors must be aimed exactly at the sun,which requires a sophisticated control system.
Second for efficiency you really want a very high temperature. That is tough on metal piping. Ceramic piping is an option that is under development.
The simple if less efficient solar panel system is much less expensive and less failure prone, but requires a lot of space.
Which one to use therefore depends on your specific application.