Provided is a washing machine including a main body having an opening and a door assembly disposed at the opening, wherein the door assembly includes a door that opens and closes the opening and an auxiliary washing unit having an auxiliary washing space in which hand-washing can be performed, and provided to pivot about one side of the door in an inside of the door. Through this configuration, separated washing spaces can be provided and separate hand-washing can be performed. Also, pressure of washing water supplied into the washing machine can be regulated so that water supply efficiency can be improved and a flow rate of the washing water can be adjusted.