With a smart meter like this one: https://www.utilities-me.com/water/11914-wetex-preview-diehls-latest-smart-metering-solutions-on-show-at-wetex you can register the minimum night flow. This minimum night flow, is normally due to leakage and can be extrapolated over 24 hours - of course it needs an adjustment, because of the changing water pressure over the 24 hours.