Buy_Sell wrote:

... I have discovered an interesting method of making as much
hot water as you would like, very efficiently on demand. If you use
your favorite search engine with the search words, 'cavitation heater'

Sounds no more efficient than electric resistance heating.

... These devices are not currently available for residential use and
there is a patent on the idea. I plan on making such a device for
my own personal use which theoretically should not violate any of
the patent laws.

The law says you can't "make, use, or sell" at patented invention
without the inventor's permission, even for your own personal use.

Nick, Registered US Patent Agent