PURPOSE: To permit a leak of water to be sensed through the level of water thereby to make it possible to prevent a serious disaster, by a method wherein the level of water to be detected by a level detecting unit is made variable by a regulating means provided between a water-leak sensor main body and a mount.

CONSTITUTION: A water-leak sensor main body 1 has three electrodes 2, 3, 4 projecting downwardly. The three electrodes 2, 3, 4 are different in length from each other so as to be able to detect two different levels of water and adapted to drive a relay disposed inside the main body 1 or a relay mounted separately by a signal representative of the level of water. A mount 5 may be bolted through bores 7 onto the sensing floor in a pump chamber. The main body 1 is mounted on the mount 5 through a regulating means sush as a screw 6, thereby making it possible to vary the distances between the sensing floor and the electrodes 2, 3, 4 respectively, i.e., the levels of water to be detected which leaks out onto the sensing floor. Thus, the level of the water gathered on the sensing floor is detected through the electrodes 2, 3, 4 to deliver to the outside a signal representing that the water having leaked exceeds a predetermined level inviting danger.