A water cleaning system (1) includes an aerobic region (90) including breeding water (9) containing organic matter and oxygen, an aerobic layer (6) linking with the aerobic region (90) and inhabited by aerobic bacteria, a facultative anaerobic layer (5) provided adjacent to the aerobic layer (6) and inhabited by facultative anaerobic bacteria, an obligatory anaerobic layer (4) provided adjacent to the facultative anaerobic layer (5), inhabited by obligatory anaerobic bacteria, and made of andasol 40, an anaerobic space (3) having an anaerobic environment, allowing the obligatory anaerobic bacteria inhabiting the obligatory anaerobic layer (4) and products therefrom to flow therein, and a tube (18) as linking means linking the anaerobic space (3) and the aerobic region (90).
