A combination water filter tank, which includes a rectangular housing, three transverse partition boards disposed in the housing and defining a first sedimentation chamber, a second sedimentation chamber, a third sedimentation chamber and a fourth sedimentation chamber, a water inlet for guiding water from an external water source into the first sedimentation chamber, a plurality of first longitudinal partition boards of different heights respectively disposed in the first sedimentation chamber, three L-shaped water guide boards respectively suspended in the second sedimentation chamber, third sedimentation chamber and fourth sedimentation chamber, a plurality of second longitudinal partition boards respectively disposed in the second sedimentation chamber, third sedimentation chamber and fourth sedimentation chamber on the middle at an elevation below the L-shaped water guide boards, and a water outlet for guiding water out of the fourth sedimentation chamber.