Nodal base demand can be ...

Nodal base demand can be determined by referring to “International Plumbing Code”. You will find various estimate of water consumption such as by bathtub, lavatory, shower head, etc. As mentioned before by some colleague in this thread, you can later use network model such as EPANET or Bentley to simulate your network and optimize production output.

Meanwhile for leakage in pipes you can start comparing your daily production and total consumption between specific time frame. More complex method you can use District Metering Area (DMA) concept where you can calculate losses on each zone of service. Further step you will need step test method and track pipe using portable leak detector after you found specific area where lekage may occur.