A faucet includes a faucet body, a switch unit and a monitoring device. The switch unit is coupled rotatably to the faucet body. The monitoring device is mounted to the switch unit and includes an angle detector, a microprocessor and an alert unit. The angle detector is for detecting angular rotation of the switch unit, and is for generating angle information. The microprocessor is for receiving the angle information, for recording a cumulative time period within which the switch unit is in an open state, and for calculating an outflow value accordingly. The microprocessor generates an alert signal for the alert unit upon determining that the outflow value has reached a predetermined threshold.