Inasmuch as Southwest North America is currently facing a "megadrought"; Water mains define a city and are the oldest urban infrastructures; Per...

Inasmuch as

Southwest North America is currently facing a "megadrought";
Water mains define a city and are the oldest urban infrastructures;
Per AWWA average distribution side water main leakage loss exceeds 20%;
The maximum consumer side water conservation achieved during the 2017 drought was ~17%;
Water main break rates in the USA and Canada increased 27% during the 2012 - 2018 time period;
ASCE has given the US potable water infrastructure a grade of "D", warning of the dire consequences of continued neglect;

we turned our attention to the design of a very low uncertainty flow calibration facility for water main metering systems up to 24" -- which would cover 85% of currently deployed water main systems -- as the first fundamental step towards water main leak detection (by volume balance) and efficient water distribution system management. See Pipeline Rules of Thumb Handbook.
"If you can't measure it, you can't manage it", per the noted management authority Peter Drucker.
The design is now complete. Metering systems up to 12" can be calibrated either on a first principles "fundamental properties" basis and/or more rapid flow transfer standard basis, and larger meters up to 24" can be calibrated using a manifold of 12" high repeatability flow transfer standards (individually calibrated on a primary standard basis).
The calibration facility uses an existing hilltop water tank to provide gravitational flow and will not interfere with normal water distribution operations. Uncertainty is better than 0.1%.