Mostly good points above about doing the math, gliding distance from shore, proper equipment (aircraft and personal).
But here is the thing...the airplane doesn't know it's over water. You can have exactly the same argument about crossing a major mountain range, flat prairies in the middle of the winter or a desert in the middle of summer. It always comes down to proper pre-flight planning and you should not have to put extra effort into flight planning if you're doing it thoroughly enough to begin with.
There is always risk mitigation required, but consider that airplanes come out of maintenance all the time and go across big swaths of water. An engine failure is just as likely the hour before a maintenance check as it is the hour after and this is where proper pre-flight checks and run-ups are worth their while.