How does waterCAD calculate the value of Flow Supplied in the reservoir ?.
WaterCAD is a demand driven software, where reservoir supplies the required flow. So the flow out of the reservoir will be equal to the total demand in the system. In below screenshot for initial 0.00 time-step total demand is 2.24 L/s, so flow supplied by the reservoir = total demand at that time-step = 2.24 L/s.
Here is learning resource guide of WaterCAD, for your reference.
Learning Resource Guide for new users of Bentley WaterGEMS and WaterCAD
Bentley Technical Suppport
What Sushma describes applies to a case where there are only demands downstream of the reservoir. In a case where there are other boundary conditions (tank or reservoir), the reservoir outflow will be based on the energy balance - the flow requires for those boundary HGLs to be true, while also satisfying other demands, controls, etc.
See also: Calculation summary: Flow Supplied, Flow Demanded and Flow Stored
Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.