With all this pressure to conserve water, pause to ponder the underpinnings: How exactly do the water lords measure how much is used? And, are they ever wrong?

Welcome to the mysterious world of flow meters – pressurized, electromagnetic, ultrasonic, etc. – and the realization that, yes, indeed, they can be wrong. To the tune of $8 million.

Turns out that water agencies in South Orange County have been overcharged $8.14 million by giant importer/lifeline Metropolitan Water District of Southern California over the years.

How did it happen? Human error, officials said.

The contractor that installed and programmed an ultrasonic meter way back in 2005 used the wrong diameter for that pipe – about an inch bigger than it actually is. This resulted in O.C. agencies being billed for more water than they actually received. For nine years.

It took years for officials in South County to figure out precisely what was going on. It was gumshoe detective work, and that work continues: There are seven more meters like this one installed throughout Metropolitan’s vast water delivery system, installed and programmed by the same vendor. Metropolitan is currently investigating them all.

Metropolitan, by the way, imports water for 19 million people from Ventura County to the Mexican border, making it possible for us all to live in this desert we call home. It’s a staggering undertaking, really.

MYSTERY

A 26-mile-long pipe transports water from the Diemer treatment plant in Yorba Linda to South County. Service Connection OC-88 – site of the aforementioned ultrasonic meter – pumps water into the South County Pipeline, where it is then slurped up by South County residents.

In 2000, Metropolitan bought $1 million of equipment from Accusonic Technologies, a company based in Massachusetts. Some in the water world like ultrasonic meters because they don’t use moving parts that can break; instead, they shoot sound waves through moving water, and use calculations involving the speed of sound to measure flow.

Most Metropolitan meters, however, are Venturi meters, which use pressure to read the flow.

In the fall of 2004, as part of a $10 million “Energy Savings Modifications Capital Project,” Accusonic installed and calibrated the ultrasonic flow meter for OC-88. Accusonic certified the accuracy of that meter, and it went into service on May 1, 2005, according to Metropolitan.

And so it went, for years. Engineers at the Santa Margarita Water District suspected something might be a bit off, but it wasn’t until they fired up their own high-tech gizmos in 2011 – which provided much more precise readings – that they had something concrete to work with.

The total amount of water that Santa Margarita’s meters said was flowing did not match what Metropolitan billed for, Santa Margarita Operations Manager Rich Kissee and his team found.

Uh oh. Was there a leak?

“It’s not unusual for those numbers to be off a percent or even two, because of variations such as when the readings are taken, and it usually balances out from month to month over the year – a little more for them one month, a little more for us another,” said Jonathan Volzke, spokesman for Santa Margarita, the biggest water district down in these parts.

“In this case, however, the readings consistently favored MET and were at or sometimes exceeded the 2 percent margin of error.”

REINFORCEMENTS

The issue took on a new urgency as water prices rose. The other South County water agencies – Moulton Niguel, Trabuco Canyon and South Coast water districts, as well as the cities of San Juan Capistrano and San Clemente – put their heads together to try to unravel the mystery.

They probed possible equipment, measuring and operations errors. They found nothing that accounted for the differences. In 2012, they asked Metropolitan for help; Metropolitan asked them to work through the middle-man – the Municipal Water District of Orange County, which buys water from Metropolitan and then sells it to them.

Municipal joined the team. The O.C. agencies completed extensive calibrations on downstream meters, checked for leaks, conducted flow tests. Still nothing.

Eyes turned northward. The O.C. agencies urged Metropolitan to test and calibrate its meter, and after the O.C. agencies said they’d pay the $16,000 cost if nothing out of the ordinary was discovered, Metropolitan agreed.

In April 2013, Metropolitan did a “volume comparison test.” It was inconclusive, Metropolitan said.

So in September 2013, Accusonic was called back in “to assist in verifying the accuracy of the meter.” The pipe was “dewatered,” inspected and measured. The electronics were tested.

And in April, Accusonic delivered its final report: Metropolitan’s meter had been over-registering flow by 3.4 percent since it was placed into service in 2005, Accusonic said.

“(T)he erroneous flow readings were caused by Accusonic’s failure to take into account the cement mortar lining on the inside diameter of the steel pipeline,” Metropolitan’s account said.

Over time, a one-inch difference added up to more than $8 million worth of water.

REFUNDS

Often, errors like these will only be refunded going back a few months to a few years – statute of limitations and all.

But recently, Metropolitan’s board agreed to reimburse the Orange County agencies $8.14 million that they were overcharged over the nine-year period. This was not a meter malfunction, Metropolitan said; it was calibrated incorrectly from the get-go.

The bulk of it will go to Santa Margarita and Moulton Niguel, at about $3 million each.

Orange County’s agencies could have tried to argue for more – interest, other fees, etc. – but agreed that this was equitable. In the end, Santa Margarita board president Saundra Jacobs sent Metropolitan a letter of thanks for its cooperation.

Metropolitan spokesman Bob Muir pointed out that, in the big picture, the error is a tiny one – amounting to less than .07 percent of annual water deliveries, and well below total distribution system losses.

“This is a rare occurrence, very rare,” said Jim Green, Metropolitan’s water systems operations manager.

But just in case, Metropolitan is testing the other seven ultrasonic meters from Accusonic for discrepancies, Green said. They are in Los Angeles, Riverside, Murrieta, Upland, Cabazon, Rancho Cucamonga and Yorba Linda. That investigation is ongoing.

Contact the writer: tsforza@ocregister.comTwitter: @ocwatchdog