Modeling several zones of a larger network

[platypus]

Hello,

I am very new to the modeling world but have recently set up a trial model of a small network in EPANET. But I have a few questions:

The network I have set up is part of a larger network. In this particular case the water mains running through this model supplies a larger network (not currently part of the model) as well. This being the case, how realistic is this model since the assumption it is making is that all water from the tank provided is exclusive to the model when in fact it is merely a small part of a larger network?

How can I make allowance for this additional demand from the rest of the network? Do I need to model the entire network first? Or is there some other way of accounting for the true water demand?

The main aim of this model is to test for fire flow compliance while implementing pressure reduction for this zone.

Cheers,
Dan