Last winter we noticed more water was being used in the middle of the night when the pumps were running than when they were off. This observation could be explained by the master meters at the water sources recording 5% too much water. For the past several years we had calibrated the master meters using a turbine meter attached to a fire hydrant near the stations and compared the amount of water flowed through the meter and the station.
This summer we assembled a truck mounted flow meter to check the master meters. The truck mounted meter uses magnetic fields to sense the velocity of the water passing through a tube with a known diameter. The meter is accurate to 0.3% and is much more accurate than the station meters. We found the venturi meter at the North Street station was over-registering by 4.1% and Perkins Row by 5.0%. We are required to keep our Unaccounted for Water below 10% so these metering errors can be a large portion of UAW.
Further testing of the truck mounted meter is needed to verify its accuracy but it was installed according the manufacturer's instructions so it should be very accurate. The meter will be used to verify hydrant flushing water use estimates during hydrant flushing this fall.