When a calamity event is modeled, the total supplied demand may be less than the normal required demand. The difference between the calculated demand and the normal required demand is a demand deficit that is evaluated under a prescribed supply level threshold. The total system demand deficit under one possible calamity event j:

Where

is the deficit demand at event j and St is the threshold of supply level. This formula provides the method for evaluating water supply level, element criticality, and modeling pressure dependent demand.