Depends upon your definition of "doable" I guess.
Capacitive discharge and flyback (Kettering) type high voltage generators have a short pulse due to the intrinsic nature of the circuits.
They are not readily modified to give a longer pulse.
Not sure how you'd tune to match the water, if your talking radio freq's then maybe a noise bridge and a receiver or scanner would tell you.
Automotive ignition coils, the later ones are usually designed for constant energy, that is the charge time is constant, take care not to charge the coil for too long and saturate and therefore overheat & burn out the coil.