>- where this can be done with a 9v battery without any circuitry whatsoever
Wrong! While just placing electrodes into the water and connecting to a 9v battery can kill some microbes, that absolutely does not kill them all. I have tried.
Also, I tried several single frequencies and none killed all of the microbes.
I also tried 2 frequencies and while 2 frequencies killed more microbes than 1 frequency did, 2 frequencies did not kill all microbes, neither did 3 frequencies.
Do not take my word for it, get a microscope and try it yourself.
>- so in my opinion
Opinions can be great, but only when based on all of the facts.