The invention relates to water purifiers and discloses a water purifier which comprises an infrared receiving head and infrared transmitting tubes. The water purifier further comprises a first controller, and a water inlet (1), a first filter element (2), a first electromagnetic valve (3), a second filter element (4), a booster pump (5) and a reverse osmosis membrane filter element (6) which are sequentially serially connected, wherein the reverse osmosis membrane filter element (6) comprises a pure water outlet and a clean water outlet, the pure water outlet is sequentially connected with a second electromagnetic valve (7) and a one-way valve (8), the one-way valve (8) is connected with a water tank (9), the water outlet of the water tank (9) is connected with a third filter element (10), the first electromagnetic valve (3) and the second electromagnetic valve (7) are connected with the first controller, and the infrared transmitting tubes are disposed on the first filter element (2), the second filter element (4) and the third filter element (10). The water purifier has the advantages that the authenticity of each filter element can be distinguished, the quality guarantee period of the filter elements can be monitored, and the outdated filter elements can be replaced.