*2.1. System Setting Curve*

The setting curve is a very useful tool in the operation and managemen<sup>t</sup> of a water supply system. This curve represents the need for energy production at the source in relation to the injected flow in the system, guaranteeing the minimum pressure at less favorable points. A distribution network does not have a well-defined resistance curve [28,29], because the curve slope changes—depending on the flow requirements and the resistance imposed on the network by user demand [30], from demand for minimum flows to demand for peak flows. However, the setting curve maintains a stable position, which is very advantageous and useful for solving problems related to water supply (see Figure 1).

**Figure 1.** Representation of the network resistance and setting curves.

For the calculation of the setting curve, a reliable mathematical model of the network should be available. Thus, it is possible to evaluate the losses in terms of various load conditions in the network. Tracking the setting curve at all times ensures that the pressure injected into the households is that which is strictly necessary to provide a good service. This produces energy savings. Similarly, adhering to the curve moderates pressure fluctuations in the network, thus reducing the negative implications of such variations in the life span of the network [29].

The setting curve is used for control purposes in pumping systems [29] and in energy optimization of water supply systems [31–33]. An approximation to the setting curve is also used as a flow modulation curve or as a setting curve for pressure reducing valves in response to changes in system demands to optimize the operation of a district metered area [34,35].

The flowchart in Figure 2 summarizes the steps to determine the setting curve when there is only one feed point. In addition to the mathematical model of the network, the minimum pressure at the nodes (*Pmin*) must also be given. This value will define the level of service to be achieved. Subsequently, scenarios for different load states, *j*, defined by peak factor *K* applied to the demand of all the nodes must be generated. Each load condition establishes an injected flow (*Qj*) in the network that requires an available head at the source (*Ha*) that ensures the minimum pressure in less favorable nodes (*Punf*). These pressures are compared with the minimum pressure until a desired very small margin of error is reached. The set of points thus obtained describes the setting curve. The hydraulic calculation for each load state is performed with DDA. It is recommended that, like in pressures, elevation and head units be meters; and the flow in liters per second.

**Figure 2.** Flow diagram for the determination of the setting curve.
