Really sad case man.

Wonder how safe are my water heaters, normally people doesnt check the ELCB thingy what, shouldnt the supply be automatically cut off if ELCB is faulty? Something is wrong here

Actually earthing should be for the body or frame of the equipment, eg electrical panels or heavy equipment metal frames you would surely see earthing cable in case of short circuit to body, and harming whoever touches the body.

For water heaters since usually the body is made of plastic, earthing cable wouldnt help. How la to easily dismantle the body if got earthing cable, furthermore metal body not cheap also.

I imagined that the electric shock happened when somehow 240vac came in contact with the water, its shorted somewhere...