An on-demand fluid transfer pump, comprising: a power head removably connectable on top of a stem that is removably connectable to a fluid supply; wherein the power head comprises an electric pump and a flow control unit configured to automatically switch the electric pump on and off; wherein the flow control unit comprises a first magnetic sensor; and wherein the stem comprises: a suction tube in fluid communication with the electric pump and the fluid supply; a fluid chamber having an inlet in fluid communication with the fluid supply and an outlet in fluid communication with a fluid dispenser; a plunger chamber in fluid communication with the fluid chamber between the inlet and the outlet; and a magnetic plunger reciprocable within the plunger chamber in response to pressure changes in the fluid chamber between a top position adjacently beneath the first magnetic sensor and a bottom position spaced away below the first magnetic sensor, characterised in that the magnetic plunger is biased to the bottom position when pressure in the fluid chamber drops to thereby deactuate the first magnetic sensor to switch on the electric pump to pressurise the fluid supply for delivery to the fluid dispenser; and in that the magnetic plunger is pushed to the top position when pressure in the fluid chamber rises to thereby actuate the first magnetic sensor to switch off the electric pump. a power head removably connectable on top of a stem that is removably connectable to a fluid supply; wherein the power head comprises an electric pump and a flow control unit configured to automatically switch the electric pump on and off; wherein the flow control unit comprises a first magnetic sensor; and wherein the stem comprises: a suction tube in fluid communication with the electric pump and the fluid supply; a fluid chamber having an inlet in fluid communication with the fluid supply and an outlet in fluid communication with a fluid dispenser; a plunger chamber in fluid communication with the fluid chamber between the inlet and the outlet; and a magnetic plunger reciprocable within the plunger chamber in response to pressure changes in the fluid chamber between a top position adjacently beneath the first magnetic sensor and a bottom position spaced away below the first magnetic sensor, characterised in that the magnetic plunger is biased to the bottom position when pressure in the fluid chamber drops to thereby deactuate the first magnetic sensor to switch on the electric pump to pressurise the fluid supply for delivery to the fluid dispenser; and in that the magnetic plunger is pushed to the top position when pressure in the fluid chamber rises to thereby actuate the first magnetic sensor to switch off the electric pump. a suction tube in fluid communication with the electric pump and the fluid supply; a fluid chamber having an inlet in fluid communication with the fluid supply and an outlet in fluid communication with a fluid dispenser; a plunger chamber in fluid communication with the fluid chamber between the inlet and the outlet; and a magnetic plunger reciprocable within the plunger chamber in response to pressure changes in the fluid chamber between a top position adjacently beneath the first magnetic sensor and a bottom position spaced away below the first magnetic sensor, characterised in that the magnetic plunger is biased to the bottom position when pressure in the fluid chamber drops to thereby deactuate the first magnetic sensor to switch on the electric pump to pressurise the fluid supply for delivery to the fluid dispenser; and in that the magnetic plunger is pushed to the top position when pressure in the fluid chamber rises to thereby actuate the first magnetic sensor to switch off the electric pump.