After a water quality control of a water tank is connected with the slightly-improved water tank, the water tank is changed into an expanded pipeline, and therefore secondary pollution is effectively avoided. Power of ball valves in the controller depends on energy provided by water inlet and water consumption of a pipe network. A filter, a chlorine control ball valve, a water overflow ball valve, a water inlet pipe, a water outlet pipe, a breathing pipe and a deep hole dirt storage tank are arranged in a tank body. The water quality controller and the water tank are connected into a whole through a communicating pipe. A manhole of the water tank is sealed, a safety valve is installed on an overflow pipe, and therefore expansion and shrinking of the tank are avoided. Through the chlorine control valve, an air chamber in the tank can be kept at micro-positive pressure, and therefore free chlorine does not easily escape out of the tank and can fully play the disinfection role. When water inlet is larger than water outlet, air, containing free chlorine, in the tank is exhausted outwards to back flush a disinfection filter element, and therefore efficiency of the filter is improved, and the service life of the filter is prolonged. A water flow slow flow zone and the deep hole dirt storage tank are arranged on the controller, and a dead water zone is moved forwards to the controller. The goal of avoiding secondary pollution of tap water is achieved without consuming electricity, adding disinfector or conducting filtering.