While modelling a simple water supply system, that includes pump, pipes,valve etc, what are the factors to be considered?

While modelling a simple water supply system, that includes pump, pipes,valve etc, what are the factors to be considered? For eg what factors need to be considered while modelling a pump. Should I cover everything, like velocity, flow rate, efficiency, losses, head, pressure etc. How to model this system? Can someone please give me a idea?