I assume that you are using commercial water flow meters. If this is the case they state in their data sheets how many litres pass through the meter per tick (or pulse). You could thus report the actual volume used per hour using millis().
You would need to connect the output of the water meter to one of the hardware interrupt pins of the Arduino (and use attachInterrupt()) so as not to miss any pulses.
Once you have detected excess usage will the manager go around 200 sites checking for wastage?
Our local water authority is tackling the same problem (determining whether leaks or wastage) by comparing the usage reported by a meter on the mains against the aggregate readings on individual meters downstream. Any discrepancy between the two readings indicates a leak. Otherwise the excess usage (i.e. waste by guests) is indicated by the individual meters.
200 meters are too many to put in, but a meter on the main and a few more on various branches would narrow the problem down to a segment of the resort.