Flow switch for fire hydrant in combined network

Dear,

we are having a combined fire and irrigation network and the idea to know where fire hydrants are opened is to put a flow switch on each fire hydrant line.
If flow switch is switched on, then the fire hydrant is being used, this will be used to know that there is a fire. When fire occurs, all irrigation facilities will be stopped and fire pumps will start. I was thinking of putting safety RTU's to take the signals from the flow switches. Maybe putting one RTU for a set of flow switches and connect all RTU's through a safety network.
What do u think first of all about this idea? and what is the criteria of combining flow switches, is it per zone? or any advice concerning wiring constraint? or any other advice?

Thanks a lot!

charbel

RTU in combined fire irrigation network

Dear,
I have considered that each RTU can cover a area having a circle of diameter = 500 m, find below a snapshot of the system? What do u think? all the RTU's will be connected to the pumping station dual redundant Safety PLC.