The present disclosure relates to a filter, which comprises a housing, a protective bushing, a magnetic bar and a filter screen. The protective bushing, the magnetic bar and the filter screen are disposed in the housing. The protective bushing comprises a cavity and a channel. The channel is disposed along the axial direction of the cavity. The magnetic bar inside the filter adsorbs metal impurities in water in the channel. The shape of the channel increases the length of the flow path of the water so that the metal impurities in the water can be guaranteed to be sufficiently adsorbed by the magnetic bar. The filter screen filters out non-metal impurities in the water. An exhaust valve provided at the top of the protective bushing balances air pressure inside the filter and outside the filter, such that the water can flow out and in smoothly.