Erica Palma got home from work one evening last winter, opened her mail and almost dropped her bags in shock.

Staring her in the face was a quarterly water bill from Miami-Dade County’s Water and Sewer Department for $5,407 — an unimaginable spike for the AT&T sales consultant whose average bill was less than $200.

“I almost cried. I was like, ‘Oh, my God,’ ” said Palma, who bought her Southwest Miami-Dade home a year ago.

But like 1,270 other residents who have taken advantage of a county ordinance passed in December that gives homeowners a one-time break on unusually exorbitant bills, Palma’s was lowered — to $141.65.

Water and Sewer customers saved more than $1.1 million in the first six months of 2012 after discovering and fixing leaks and showing that the bill in question was more than six times their average bill. Ten other customers took advantage of an amendment to the one-time adjustment for a water bill, saving a total of $10,293, after submitting evidence that they had no leak, or didn’t leave a hose or water tap running.

The measure got a chilly reception from Water and Sewer Director John Renfrow, who is struggling through a third month of negotiations with federal authorities over how to repair more than $1 billion worth of decaying sewage lines, water lines and treatment plants. County leaders have already warned that water rates are certain to rise, and new bonds for hundreds of millions of dollars could be on the way.

Renfrow said he was concerned that his department could take a hit of $2 million a year.

“While we understand that there need to be procedures in place to provide relief for extraordinary situations, it remains a balancing act whereby each dollar lost to water bill credits means that there is less funding for improvements to the department’s aging infrastructure,” Renfrow said. He urged residents to be proactive and check for leaks.

County Commissioner Lynda Bell, the bill’s sponsor, said she is well aware of the county’s water and sewer shortcomings, but that constituents deserve a relief valve.

“People had unexplainable high bills. We had different residents approaching us,” she said.

In some instances, homeowners’ bills run high due to theft. It usually occurs when they are away on vacation or at work. Commissioners and the county staff debated whether a creditworthy customer should be held responsible in cases of theft. They decided to give them the one-time amnesty.

“There is water stealing going on — we know that,” Bell said.

Bell’s push to give homeowners a break began last year after the county took a look at thousands of complaints that had accumulated over the years. In addition to theft, some bills ran high due to hidden underground leaks. Sometimes, the sudden upsurge in water use couldn’t be explained.

The new rules were tailor-made for Palma, 25, who lives with her fiancé in a 1,928-square-foot home. She said hiring a plumber who found an underground leak behind a wall in the home, then filling out the proper forms and affidavit, was a “pain,” but a worthwhile one.

“It took a while, but in the end they lowered my bill,” she said.