The remaining five accounts seemed OK, the audit said. The tendency to estimate bills—and to overestimate those amounts—appears to be the core of the problem. There are 411,000 active accounts, of which 18,266 had been estimated for a year or more, according to auditors (the bureau says it's more like 10,000). That's at least 2.5 percent of the total. In its response to the new audit, the bureau noted that 2,222 city accounts had been overbilled and 163 underbilled, while in the county, 2,747 were overbilled and 140 were underbilled. Taken together, then, the bureau is about 15-20 times more likely to overbill customers as to underbill them. Amato could not explain that tendency. In 2008, John Brewer, who was in charge of billing for the system, estimated the bureau had an error rate of less than 0.2 percent—two errors in 1,000. Amato says Brewer retired about a year ago and that the bureau is working to fill his position. In 2009, 88.4 percent of the meters were read; in 2011, 92.8 percent, which means 7.2 percent were not read that year—about 56,000 meters. Amato says there are multiple reasons for the unread meters. "Some are inaccessible," she says. "They can't be found. We have increased the number of staff dedicated to that. Now we start dropping a new meter in whenever the old one is gone." Others who have inside meters that are supposed to transmit a reading to a box hanging outside (but don't) have been getting forms that instruct them to read their own meter and call in the readings. This is a technique in common use in many cities. It is new to Baltimore. "The [billing] system is 40 years old," Amato says. "Time for the upgrade." Says Stewart: "It's too big for them to fix overnight. It'll take years for them to fix this problem."