Create correct pressure in starting node

Hi! I am currently developing a program to simulate if water demand during a fire event is satisfied in planned water distribution networks. I am using the WNTR package in Python to create the planned network based on data from the CAD/BIM software used.
As the new networks are connecting to an existing node, and i wish to use a given pressure in the node, what would be the best solution to use to get the most correct hydraulic behaviour? The thought is that the owner of the network gives the initial pressure in the node, and this is used for the simulation of the planned expansion of the network.
Is it possible to set a pressure at a node, assuming it has constant supply from a reservoir, just to get the pressure i need at this point, or do i need to add a virtual reservoir to make it work?

Hope the problem makes sense, and hopefully anyone has some input!