Water utilities everywhere struggle to reduce real water loss using a variety of tools from acoustic leak detection, to water audits, to pressure anomaly detection, to ground penetrating radar, to pressure management. Each of these addresses a portion of the problem and there is no single perfect solution.
Another issue lies in the personas who are asking and answering the question. Usually the decision maker (i.e. design engineer or system operator) will ask the modeler, “Is this model calibrated?,” and expect the modeler to answer yes or no. What should happen is that the modeler should show the work that was done to calibrate the model to the decision maker and ask, “Do you think the model will meet your needs?”