Any time you are dealing with changes to an existing system - especially with water - there are a number of factors to consider. I know I am bound to overlook one or more in this reply, so hopefully there will be others who can and will answer as well. In bullet style format, you will need to present/consider:
incoming pressure and pressure drop through the system (constant supply? adding to current supply?)
flow rate needed at each exit point vs. incoming flow rate (important is "schedule" for exit points i.e. what happens if everyone flushes toilet at same time)
both above also determine pipe sizes - compare to existing for connection point
potential for galvanic reaction or same pipe materials used?
any chemical concerns/changes to water for drinking vs. process water (softening, filtering, etc.) - this is a large topic in itself, but I'm assuming a municipal supply, no special needs in building
current buillding layout vs. proposed pipe routing
costs and method of connection (flanged? threaded? soldered? - each have different costs associated with them)
additional or special valving required? - check valves, etc.
fire water supply to sprinkler system
environment for pipe - need insulation to avoid sweating in humid conditions?
potential maintenance concerns or accessibility
While I don't doubt there are others, this is all that came to me in the few minutes I had to answer. Hope this helps.