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.