The problem here is that in order to change a microwave to UV, you need to add energy to it. Generally, diffraction and distortion of light waves don’t change what part of the spectrum they’re on - that’s why water doesn’t change the color of light passing through it. The wavelength changes, but critically, the frequency doesn’t, and frequency is really what defines the energy of a given photon, which in turn defines the part of the spectrum it’s on. So if the microwave is turning into UV somehow, that means it has to be stealing energy from the container or food, which would make the food colder.

I’d expect the only UV rays that would be emitted within a properly functioning microwave would be from the appliance light bulb inside of it if it’s still an incandescent design or from the food/container itself if it gets sufficiently hot. I’m not sure of any mechanism in the magnetron that would make UV in any substantial amounts.

Yup. This is why the whole ‘States rights’ argument is absolutely bullshit. The only states trying to bring the federal government in to usurp other states’ authority were the slave states.

You’re probably right about it not saving enough money, but the math you did above assumes one water heater per person.

The median household in the US is about 2.5 people. So $34 per year per person becomes $85 per household. Reducing the time to break even to 17.3 years.

Still longer than that water heater is likely to last, but not quite as bad.