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 5provided 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 andosol 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.
