A simple method is given for estimating the continuous PQ disturbance level at a site. It is based on determining a "Voltage Distortion Increment" (VDI) for each segment of the network and then adding the VDIs from a given site back to an upstream site where levels are taken to be zero. The VDI is conveniently expressible in the form of S(MVA) times length (km), where "length" correspond to the physical length in the case of MV overhead lines and an equivalent length for other components. The method is verified by a comparison with field survey data. The voltage distortion figures assist in the choice of PQ monitor placement and for estimating levels at unmonitored sites.