"The business went downhill," she said. "When I got involved with the water bills, I started to pay more attention to that than to my business."

Stewart estimates she reviews 10,000 to 20,000 individual bills per quarter. She arranges them in Excel spreadsheets so she can watch how businesses' bills fluctuate. She spotted it when Dunbar Middle School's bill spiked to $100,000, when the Maryland Zoo in Baltimore received a $200,000 bill and when Good Samaritan Hospital was overbilled by six figures. She watched wild, seemingly impossible, variations in bills at the Marriott Waterfront Hotel and the National Aquarium.

"A lot of hotels and big businesses, they're just paying them," she said. "The bills come in, and they just pay them."

If she weren't at Violetville Park, checking out the buried meter, she said, she would be at home going through the files: It's what she does all day, every day.

"I don't think anybody has ever collected as much information about this as I have," she said.

At first, his wife's intense interest in water bills concerned him, Terry Stewart said. But then he realized she was on to something. When you see an injustice in life, you should fight it, he said.

"I said, 'Honey, you're right," he recalled.

Linda Stewart's efforts have attracted a following. She said she is contacted nearly every day by someone in Baltimore who has received an usually high bill. Since the audit came out this week, she's been getting calls and emails nonstop.

Holly Knott, a married mother of two from Morrell Park, found Stewart through her website. Knott said she found out last month that her water bill had suddenly doubled — as had those of many of her neighbors — and they've been getting the runaround from the city. When she posted a blurb about it on Facebook, her friends all told her the same thing: Contact Linda Stewart.

"I sent her a message, and we've been talking throughout this whole process," Knott said. "She has a lot of good information. I've learned a lot from her."

Stewart's advice for such residents is simple: Never give up. Often, Stewart said, overcharged residents have to go to great lengths to get a refund, including having to prove they don't have a leak, waiting weeks for responses and sometimes needing to take time off from work for a downtown meeting with city officials.

"You've got to keep fighting," she said. "It's not harassment. It's persistence."

The comptroller's meter

Despite Stewart's efforts to publicize the issue, the audit would never have happened had Comptroller Joan M. Pratt not gotten involved.

Pratt said the issue came to her attention only after one of her former staff members received an unusually high bill — and then the comptroller got two herself.

Twice, Pratt said, she received bills for $800 because of a faulty meter.

"That's very expensive for a single person," Pratt said. "It really made me pay attention to the issue. My water bill was unusually high; it made me want to take a look and see if this was an isolated incident or if it's pervasive throughout the city."

The audit examined water bills for 70,000 households over three years and found that 65,000 were likely overcharged and 53,000 showed no record of any adjustment. The audit also found that nearly one-third of homes with new meters had not received any bills over the three years. Moreover, 57 homes that were included in the city's tax sale because of unpaid water bills had bills that were based on estimates, not meter readings.

MayorStephanie Rawlings-Blakeresponded to the audit's findings by saying that her administration had inherited the problem of aging, faulty infrastructure in the city's water billing system. Her administration has pledged to try to remedy the problems by hiring a contractor for more than $100 million to replace the meters, but cautions that it will take years to revamp the water meters and the billing system.

"If you don't have a modern billing system, you're going to continue to have these types of problems," Kocher said. "We have a [Atari] Pong system when what we need is post-Wii."

Stewart said she realizes changes will be years in the making, and that aging infrastructure and meter systems are problems nationwide. Still, she said, she thinks City Hall could do a better job of handling the issue.

For one, she said, Baltimore should stop placing liens against residents' homes for unpaid water bills until officials are sure the billing system is correct. And, she said, the city should commit to replacing 10 percent of its meters every year. She said she's glad the city finally appears to be taking the issue seriously but wonders why previous administrations haven't done more.

"They've known this has been going on for years," she said. "They need to start replacing everything."

An earlier version of this story may have implied that all city water users' bills were examined in the audit. The Sun regrets the error.