It is an object of the present invention to provide an effective technique for achieving a higher level of water quality control in a water treatment apparatus. Representative water treatment apparatus according to the present invention may include a purifying section, a sterilizing section, a water storing section and a water quality detection sensor. The water quality detection sensor is immersed in the water storing section. The water quality detection sensor not only serves as a means for detecting the quality of water in the water storing section, but also as a means for detecting deposition of biomembrane on the detecting section of the water quality detection sensor due to deterioration of the sterilizing performance of the water storing section. As a result, an efficient water quality control system can be realized.