Deploy pressure and flow ...
Published by Robert Welke, IRRIGATION PUMPING ACADEMY
Deploy pressure and flow data loggers to straegic locations in the network over say a week.
Construct an hydraulic network model using any of the commercially available water network analysis software packages. (I use EPANet because its free)
Massage the model to emulate the field data at any one time will reveal system performance and efficiency. Will reveal bottlenecks.
Its very labourious and time consuming, but this approach has always yielded good results for me.
In my opinion, seek expert advice and assistance.