When in use, never spray water directly onto the heater casing.  Ensure there is an ELCB  (earth leakage circuit breaker) built in.  If not, have a qualified electrician install one.  Make sure the ELCB is functioning. Do this once a month. Press the button marked “Test”, the electricity will switch off immediately. Press “Reset” to restore the power.  Ensure your home’s main ELCB is also in working order. Test it regularly.  Only a qualified electrician should install/repair the heater.  Always buy from a reputable brand.