For optimal water use efficiency, it is useful to check the irrigation output matches what the system was designed for.
When your irrigation is running, select at least 9 sprinkler heads from various locations (the beginning, middle and end of the line for at least 3 lines) and place each one into a bucket. Run the water for 2 minutes and measure the amount of water that is captured in the bucket and calculate the output. The measurements should be within 5% of each other for an efficient system.
Inline pressure gauges can be used for the water pressure in your irrigation lines. Once again, checking at different locations will provide an overview of any variation or inefficiencies in your system.
As discussed in water quality, both salts and particles can build up over time and cause problems in your pumps and lines. Monitor your water quality and if you have magnesium, calcium or particles present in high levels, pay particular attention to your pressure and fittings. Check sprinkler heads regularly to reduce blockages and if necessary, invest in a system to reduce the build-up of salts/particles.
The farm water quality and treatment factsheet from the NSW DPI includes information on treating hard water.