The invention provides a filter and a water treatment system, and mainly relates to the field of agricultural irrigation. The filter comprises a shell and a filtering assembly, wherein the filtering assembly is arranged in the shell, a first cavity is defined by the filtering assembly, and a second cavity is formed between the filtering assembly and the shell; the filtering assembly is connected rotationally with the shell; a water inlet, a water outlet and a sewage outlet are formed in the shell, the water inlet and the sewage outlet are communicated with the first cavity respectively, and the water outlet is communicated with the second cavity. The filter increases the concentration of dirt in the sewage discharged from the filter and saves the sewage discharging time. The water treatment system is beneficial to the improvement of the sewage discharging efficiency in the water filtration process.