250 LPH DM Water Plant This automatic plant watering system will automatically water your plants when it senses that they are thirsty. This smart watering system uses an ultrasonic sensor to detect the soil moisture level. The sensor sends a signal to the controller which then activates the pump and starts the flow of water. As soon as the soil reaches its optimum moisture level, the flow stops. The system can be programmed to activate the pump every day or weekly.