A cleaning system (1) for water is constituted so as to be provided with: an aerobic region (90) in which breeding water (9) that contains organic matter and oxygen are present； an aerobic layer (6) linked with this aero Die region (90) and in which aerobic bacteria make their habitat； a facultative anaerobic layer (5) provided adjacent to this aero Die layer (6) and in which facultative anaerobic bacteria make their habitat； an obligatory anaerobic layer (4), which is provided adjacent to this facultative anaerobic layer (5), in which obligatory anaerooic bacteria make their habitat, and which is constituted b y andosol (40)； an anaerobic space (3), which is an anaerobic environment into which obligatory anaerobic bacteria making their habitat in the obligatory anaerobic layer (4) and products thereof can flow； and a tube (18) as a linking means for this anaerobic space (3) and the aerobic region (90).
