If the grid goes down you can build one of these to serve your hot water requirements :

 

Further Study
I built a water heater out of used parts and used a Stovetec Rocket stove to start the thermo siphoning process. Coil vid : https://youtu.be/-l-lMKlVFpA
SilverFire Survivor Stove : https://www.practicalpreppers.com/online-shop/cooking-solutions/silverfire-survivor-rocket-stove-detail-view
Radio Frequency Generator, How to Burn Sea Water