Epanet hydraulic analysis allows for two different ways to model water demands (ie. consumption) at network junction nodes. Demand Driven Analysis (DDA) requires that the demands at each point in time are fixed values that must be given, regardless of the nodal pressures and connection flows produced by a hydraulic solution. This has been the classic approach used to model demands, but it can result in situations in which necessary demands are satisfied in us with negative pressures - a physical impossibility.
An alternative approach, known as Pressure Driven Analysis (PDA), allows the actual demand delivered to a node to depend on the pressure of the node. Below some minimum pressure, demand is zero, above some service pressure, the total required demand is given and between the demand varies as a power law function of the pressure. Using PDA is a way to avoid positive demands on us with negative pressures.
The EPANET hydraulic analysis options are used to select a demand model choice and provide the parameters used by the PDA