A water level controller for a hydroponic system includes a float shifting upward and downward with the culture solution, a first magnetic attraction element and an inlet valve for feeding in the culture solution. The float includes a seal and a second magnetic attraction element. The seal closes the inlet valve to stop feeding in water when the float ascends to a high water level, and moves way from the inlet valve to start feeding in water at a low water level. The second magnetic attraction element attracts the first magnetic attraction element to keep the seal closing the inlet valve at the high water level and to keep the seal moving away from the inlet valve at the low water level, until the buoyancy of the float is larger than the magnetic attraction between the second and the first magnetic attraction element thereby causing escape from each other.
