The only thing that's certain is that each report is different. I've also had the opportunity to meet or speak to many operators, bookkeepers, city clerks and public works superintendents who provide information for the water use reports. The one thing they have in common is a great attitude about their work. I'm always impressed with how well these people handle the challenging tasks of operating a water system. Because of their efforts at keeping water records, we all know more about identifying water loss.
All systems experience some water loss as an ordinary part of operation.
Water loss is also called 'unaccounted for water' to distinguish it from losses that occur for known reasons, such as for water treatment processes or hydrant flushing. What is a reasonable percentage for your system depends on the type of treatment required, the condition of your system, and how much of your use is metered. The first thing to do is to have believable figures. There's no use chasing down leaks if your master meter is grossly overregistering, or if your sales figures are erroneous. Check that all metered uses have been properly accounted for.