A water treatment device includes: an insulating divider which divides a space inside a water tank into two treatment vessels adjacent to each other in a horizontal direction, and includes a current carrier which is able to energize water in the two treatment vessels; a treatment unit including a pair of electrodes, a power supply, and a power supply controller; a water supplier which supplies water to each of the treatment vessels; and a draining member which drains water from each of the treatment vessels. The treatment unit includes a detector which detects a level of water in each of the treatment vessels based on an index corresponding to a current value between the pair of electrodes.