Abstract: A monitoring system for monitoring resources such as water in a bore having an air column extending from a wellhead to a surface level and a resource column extending from the surface level to an extraction inlet includes a sensor unit and a base unit. The sensor unit includes a sensor mounted within the bore and including a transmitting unit for transmitting at least a single sound pulse formed of a pulsed sinusoidal waveform into the bore and a receiving unit for receiving a return signal representing the single sound pulse reflected from the water surface level. The base unit uses the measured round trip time to determine an air column length from the sensor to the water surface level and a water column length from the water surface level to the extraction inlet and, from a cross sectional area of the bore, a water resource value representing a volume of water contained between the water surface level and the extraction inlet.