Cold water recycling device for bathroom

A cold water recycling device for a bathroom comprises a hot water tank, a tap water inlet pipe used for conveying cold water to the hot water tank and a hot water outlet pipe used for outputting hot water from the hot water tank. A return pipe used for enabling cold water in the hot water outlet pipe to flow back to the tap water inlet pipe is arranged between the tap water inlet pipe and the hot water outlet pipe, a temperature sensor I used for detecting the temperature of water in the hot water outlet pipe is arranged on the inner wall of the hot water outlet pipe in an embedded mode, the temperature sensor I transmits detected temperature information to a microprocessor, the microprocessor controls opening and closing of a switch arranged on the hot water outlet pipe, opening and closing of a solenoid valve and switching-on and switching-off of a water pump according to the received temperature information, the solenoid valve and the water pump are arranged on the return pipe, and therefore backflow of t