A water filtration system , comprising: an integrated composite filter cartridge having a water inlet , a purified-water outlet , a purified-water return port , a pure-water outlet and a sewage discharge port , wherein the integrated composite filter cartridge comprises a pre-filter cartridge located between the water inlet and the purified-water outlet, a fine filter cartridge located at the purified-water return port, and a post filter cartridge located at the pure-water outlet; a water-intake pipe communicated with the water inlet ; a purified-water pipeline configured to communicate the purified-water outlet and the purified-water return port , the purified-water pipeline being provided with a purified-water external port and a first valve configured to control blocking and unblocking of the purified-water pipeline ; a pure-water pipeline communicated with the pure-water outlet , the pure-water pipeline being provided with a pure-water external port and a second valve configured to control blocking and unblocking of the pure-water pipeline ; and a sewage discharge pipeline having a first end communicated with the sewage discharge port and a second end communicated with an outside, wherein the water filtration system is configurable in a first arrangement, in which the purified-water pipeline is unblocked and the pure-water pipeline is blocked, to direct water to the purified-water external port ; and the water filtration system is configurable in a second arrangement, in which the purified-water pipeline , the pure-water pipeline and the sewage discharge pipeline are unblocked, to direct water to the pure-water external port . an integrated composite filter cartridge having a water inlet , a purified-water outlet , a purified-water return port , a pure-water outlet and a sewage discharge port , wherein the integrated composite filter cartridge comprises a pre-filter cartridge located between the water inlet and the purified-water outlet, a fine filter cartridge located at the purified-water return port, and a post filter cartridge located at the pure-water outlet; a pre-filter cartridge located between the water inlet and the purified-water outlet, a fine filter cartridge located at the purified-water return port, and a post filter cartridge located at the pure-water outlet; a water-intake pipe communicated with the water inlet ; a purified-water pipeline configured to communicate the purified-water outlet and the purified-water return port , the purified-water pipeline being provided with a purified-water external port and a first valve configured to control blocking and unblocking of the purified-water pipeline ; a pure-water pipeline communicated with the pure-water outlet , the pure-water pipeline being provided with a pure-water external port and a second valve configured to control blocking and unblocking of the pure-water pipeline ; and a sewage discharge pipeline having a first end communicated with the sewage discharge port and a second end communicated with an outside, wherein the water filtration system is configurable in a first arrangement, in which the purified-water pipeline is unblocked and the pure-water pipeline is blocked, to direct water to the purified-water external port ; and the water filtration system is configurable in a second arrangement, in which the purified-water pipeline , the pure-water pipeline and the sewage discharge pipeline are unblocked, to direct water to the pure-water external port . <EOS>