Hi,
I can't find a forum for water heaters. There should be one.
there is an interesting water heater done with the water hammer effect. some videos on youtube: fuelless water heater.
Also I have found this site http://www.anzwers.org/free/wroclaw/free_energy.htm talking about a resonant heater so simple to do that I wish some people here try it.
Your comments please.