Abstract: A water filter sand level sensor is positioned inside a water filter and detects if a sand level in the water filter is above or below a critical level. The sand level sensor is connected to an indicator outside the water filter that provides a visual or audible signal regarding the sand level in the water filter. The sand level sensor may be a light dependent resistor detecting light from a light emitting diode and having a resistance that decreases with increasing incident light intensity. The sand level sensor also may be an ultrasonic transducer transmitting ultrasonic energy bursts vertically down through the water filter to the sand level and determining a time difference between a transmitted and a reflected signal.