Abstract: In a swimming pool having an electrically powered pump for circulating water, a portion of the water in the swimming pool is directed into a chamber in communication with the pool, so that the level of the water in the chamber is the same as the level of the water in the pool. The circuit supplying electrical current to the pump includes a switch mounted in the chamber. A float supported by the water in the chamber is mechanically connected to the switch in such manner that the switch permits current to flow to the pump, when the float is supported at or above a predetermined level. A drop in the level of water in the pool causes a corresponding drop in the level of water in the chamber, so that the float falls and actuates the switch causing the pump to be disconnected from its power supply.