Grounding an immersion heater
Figure 1. Random immersion heater image from Amazon.
Any immersion heater for your application must have a plug with an earth pin. The earth wire must connect the earth pin directly to the element's protective tube.
This method of earthing when used with appropriate circuit breaker and RCD/ELCB/GFCI protects the user from electric shock. It should not be compromised.
If the unit is supplied with a two-pin plug then don't buy it.