Within your park, are there shut off valves that section off your park? If so, do valve checks regularly until you can get your individual meters in. Transversely, ask the city to give you data on their master meter (if its radio) once a month or whatever interval, at like 3 in the morning, if there is high usage there is a leak or a bunch of them. Do you know how to spot a leak on the surface ? It sounds easy enough, it can be harder than it sounds.
Really tall green grass in a line where everything else is short and dead dead. Sink holes in weird places. Puddles in July in the heat... oh, and if your streets are paved and they are sinking at the seam lines in the center (if they are wide enough for two lines of asphalt) your main lines should be checked by a professional. Your manager / maintenance person should be walking property daily to check on this kind of thing along with trash pick up and tagging cars for illegal parking, etc.. Also alert your residents to look for leaks - any mushy ground around or under their home, and encourage them to let the office know asap so you can get it handled. That multiples the eyes on the ground
We had a resident cover a leak with a tarp, a disk weight from a weight lifting bar, and a pallet, to "stop the leak." but they didn't tell me about it until I went and asked them what the pile was for.
Had another one that decided to skim coat a brick walk way - next to a 40 year old Cedar tree - which if it was a normal scenario, would have drank the water, in order to keep his wife's feet dry to their car... never thought to talk to the office - and it was their main water line, it was affecting the pressure in their home, and leaving a mess and had been that way at least a year and they said nothing... they also tried to "fix it. "
it takes all kinds.