Leaking Hot Water Unit
Go to your hot water unit and locate the pipe closest to the bottom of the unit – this will be the cold water inlet pipe, it is where the unit recieves its water and it should have a black knob fitted on the line near the tank. Turn the knob in a clockwise direction until it closes. This will stop any more water from going in to the unit. The leak may continue for a little while but without the water supply coming into the unit the tank should quickly depressurise which will slow the leak considerably.
Next, go to your electrical switchboard and locate the hot water circuit switch. The great majority of homes have a separate circuit for the hot water unit and this circuit should be marked as such. Flick the switch marked hot water to the ‘off’ position. Once you have done this you have now isolated both the water and power supply to the unit. If you don’t islolate the power supply and the unit does drain dry the element will remain active and will overheat because there is no longer any water left in the tank for it to heat.