Check your mailbox: Atlanta’s Department of Watershed Management may have a refund coming your way.

Beginning next week, 541 customers are expected to receive a collective $737,372 in refunds for overpayments on water bills, pending approval by the Atlanta City Council. Thirty-six of those people are receiving more than $5,000 apiece. And two in one city district will see a combined $46,632 coming back to them.

“We hope this will establish confidence not just in (our) meters, but in our staff,” Watershed Commissioner Jo Ann Macrina said. “And we know there is still room for improvement.”

The refunds are a result of the Watershed Department’s 2011 small meter audit, which reviewed nearly 160,000 water meters installed between 2007 and 2009 with the aim of improving billing accuracy, identifying leaks and cutting the time it takes to read meters. The department serves 180,000 accounts in Atlanta and in neighboring jurisdictions.

But the $35 million project didn’t go smoothly, as some Atlantans were shocked to see their water bills spike. For example, Wilda Cobb of Buckhead said she saw her monthly payments soar from $30 to as high as $7,000 for a single month in 2011. Outlandish bills soon became headline-grabbing news across the city, which has among the highest water and sewer rates in the country to help pay for $2 billion in sewer upgrades required by federal regulators.

Complaints prompted Mayor Kasim Reed to call for the audit, which found that nearly two-thirds of the meters had problems, such as broken or ill-fitted meter lids. But few of those issues affected billing, Macrina said. The majority of the meters served homes.

The audit also discovered that 99 percent of water usage was accurately reported, with just 0.7 percent of meters — or 1,085 — found to cause billing errors. About 520 of those faulty meters resulted in overbilling between 2007 and 2013.

The Watershed Department’s Mohamed Balla said just a handful of the refunds are going to customers who lost appeals to the city’s Water and Sewer Appeals Board.

Customers were also underbilled to the tune of $981,000, but the department is not seeking payment, Macrina said, as it’s a fraction of the agency’s $200 million to $250 million in annual revenue from residential use. City officials are also refunding late payments and paying 7 percent interest to customers.

Macrina said that because properties have changed hands, her department has spent months reviewing tens of thousands of individual bills to determine who overpaid and when. Therefore, refunds will be issued to people who may no longer live at the address where the overbilling occurred.

“It was meticulous work,” she said, “but it was very important that we got this right.”

Cobb believes she’s among those who were overbilled but does not yet know whether she’s getting a refund. Her problems began in 2011 when her monthly bill jumped from $30 to $800 in a single month, followed by bills for $1,200 and then $7,000. But no leaks were ever found, she said.

“I’m a fairly reasonable, logical person and said ‘something is wrong here,’ ” Cobb said. “I called the city, and they would never do anything or admit any fault until I talked to the press.”

Cobb’s staggering water bill issue, which culminated in $10,000 with fees, was featured in a CNN article that year. It was then that the Watershed Department installed another meter, which immediately fixed the problem, she said. City officials dropped her charges to $800, which she paid.

Cobb hopes she’ll be among those receiving a refund years later from the city.

“Maybe I’ll get lucky,” she said.

The department is working to win back the confidence of Atlantans, having long faced criticism stemming from myriad problems, including aging infrastructure, unforeseen high water bills and the city’s former reliance on estimated water use to determine the amount due.

Some have criticized the Watershed Department for turning to automated meters, which transmit water usage data electronically back to the agency’s system. But the audit found that just 42 meters overbilled or underbilled because of faulty data transmission, Balla said.

Many customers, Watershed officials say, saw bills rise because the new meters gave accurate readings of usage to historically underbilled customers.

Still, a year ago, the department refunded $7.5 million to 3,490 customers who used irrigation meters to limit their sewage bills and were erroneously overbilled between July 1, 2008, and Sept. 30, 2010.

The agency made several changes as a result of the small meter audit, Macrina said in June. For one, the department is lowering the threshold that triggers a meter investigation from usage exceeding 100 percent of the monthly average to 50 percent of normal use.

“We can’t just fix the problem,” she said. “We have to ensure it doesn’t happen again.”

The Atlanta City Council will vote next week whether to approve about $327,400 in refunds, which is the amount owed to customers whose refunds exceed $5,000 and therefore require legislation. At that time, the department plans to launch a website, www.atlantawatershed.org/MBAA, and call center (404-546-7363) where people can check to see whether they are owed a refund. The website and phone number are not yet active.

The agency is now reviewing larger meters primarily used in commercial and industrial properties.