Water purification system

The invention relates to a water purification system which comprises a water production pipeline, wherein the front end of the water production pipeline is connected with a raw water inlet pipeline; the water production pipeline is sequentially provided with a prepositive treatment filter element, an RO (reverse osmosis) membrane filter element and a postpositive filter element; the RO membrane filter element is connected with a concentrated water outlet pipe; the tail end of the concentrated water outlet pipe is connected with a concentrated water tank; the concentrated water tank is provided with a concentrated water outlet and a water discharge port; the water production pipeline in front of the RO membrane filter element is provided with a mixed flow valve I; and the mixed flow valve I is connected with the concentrated water outlet through a concentrated water inlet pipeline. No matter how the water utilization of the user changes, the mixing ratio of the concentrated water to the raw water in the system is always fixed, so that the overall system has excellent stability. Besides, the concentrated water from the RO membrane filter element does not completely enters the circulating loop, but enters the loop according to a certain proportion, and the mixed water concentration is almost equal to the raw water concentration, thereby avoiding costing the service life of the RO membrane.