NOVELTY - A water supply system comprises supply controlling valve which controls transfer to first processing tank (30), second processing tank (10) and separation tank by supply line, taking-in controlling valve which controls transfer from each of first processing tank, second processing tank, separation tank and wastewater source by taking-in line, and control part which controls operation of supply controlling valve and taking-in controlling valve to transfer with activated sludge of first processing tank, second processing tank and separation tank.    USE - A water supply system for wastewater treatment installation (claimed).    ADVANTAGE - The water supply system provides wastewater treatment installation which can perform efficient removable activated sludge treatment of nitrogen and phosphorus of wastewater.    DETAILED DESCRIPTION - A water supply system comprises first processing tank (30), second processing tank (10) and separation tank which separate activated sludge from wastewater and implement activated sludge treatment, pump apparatus (40) which transfers wastewater and/or activated sludge, supply line which transfers to first processing tank, second processing tank and separation tank from discharge port of pump apparatus, supply controlling valve which controls transfer to first processing tank, second processing tank and separation tank by supply line, transferable taking-in line which separately transfers wastewater and activated sludge to intake of pump apparatus from each of first processing tank, second processing tank, separation tank and wastewater source, taking-in controlling valve which controls transfer from each of first processing tank, second processing tank, separation tank and wastewater source by taking-in line, and control part which controls operation of supply controlling valve and taking-in controlling valve to transfer with activated sludge of first processing tank, second processing tank and separation tank. An INDEPENDENT CLAIM is included for a wastewater treatment installation.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of the wastewater treatment installation. (Drawing includes non-English language text).    Second processing tank (10)    Aeration apparatus (11, 31)    Stirring apparatus (12, 32)    First processing tank (30)    Pump apparatus (40)