BANGOR, Maine — The Bangor Water District is planning its first water rate hike since 2011 in a bid to replace aging infrastructure.

The water district’s board has not approved the planned increase, but General Manager Kathy Moriarty told the trustees this week it would be about 9 to 9.5 percent, according to rough estimates.

“We’re still working with it,” she said.

Under the current rate structure, the average residential customer pays $57.97 per quarter, according to Moriarty. The increase represents about $1 per month extra for that customer, she said.

The board will discuss the exact amount of the increase during a work session next week and vote on the issue during a March 17 meeting.

With approval from the Maine Public Utilities Commission, the increase would go into effect July 1. A public hearing is scheduled from 5 to 7 p.m. May 14 in the council chambers at city hall.

Water district trustees also plan to address the City Council during its March 9 meeting. Moriarty said the water district would notify customers of the rate change through its newsletter and direct mailings after it’s approved.

The system’s largest customers will be invited to a special meeting March 26. Moriarty said she had already notified Hampden Water District Superintendent Jamie Holyoke.

The Hampden Water District is Bangor’s second largest customer, consuming 104.37 million gallons last year. Holyoke was not immediately available for comment Thursday.

The proposed increase would cost Eastern Maine Medical Center an additional $16,000 per year, according to Facilities and Emergency Preparedness Administrator Joel Farley.

“Like any organization, EMMC must must weigh increased expenses against our ability to reinvest in other areas,” he said in a statement.

EMMC is the water district’s third largest customer, consuming 55.36 million gallons last year.

Moriarty said the water district has not yet estimated how much additional revenue the rate increase will bring, but district officials hope to use the extra income to replace the aging infrastructure.

PUC rules implemented since the water district’s last rate hike allow public water suppliers to create capital reserve or infrastructure renewal accounts so long as no more than 1 percent of each supplier’s total revenue goes into the account.

In Bangor, the water district estimates that 1 percent of total revenue with the increase will be about $553,000 a year. That won’t come close to replacing all of the system’s aging equipment, Moriarty said.

Sixty miles or 28 percent of the system’s water lines are more than 100 years old, according to the water district. The estimated replacement cost for that exceeds $60 million, according to water district officials.

Replacing that pipe, which is past its useful life, is critical to reducing the number of leaks in the water system that are often costly to repair, Moriarty said.

Since the beginning of 2007, the system has experienced 235 leaks, the most expensive of which cost $47,945 to repair. The water district has spent $710,545 repairing leaks since the start of 2007, not including 2012 — for which financial data was not available.

Of the 21 line breaks the district repaired last year, 40 percent involved pipes that were between 100 and 109 years old, according to the water district. There were no failures in pipes that were less than 60 years old, the district reported.

Another 77 miles of the water district’s 214 miles of water pipe is more than 50 years old, according to the district.

The planned rate increase comes as the water district anticipates the loss of its largest customer, the Penobscot Energy Recovery Company in Orrington, which consumed 137.79 million gallons of water last year.

The Municipal Review Committee, a group representing the trash disposal interests of 187 Maine communities, plans to develop a $60 million solid waste recycling and process facility in 2018 in Hampden to replace PERC.

According to the committee, PERC will no longer be viable that year because of the expiration of an agreement that has Emera Maine purchase electricity produced at the plant at above-market rates.

Moriarty told the water district’s trustees the new facility in Hampden will indirectly use Bangor water through the Hampden Water District, but the amount consumed by the new facility is expected to be less than PERC.

Since the water district’s last rate increase in 2011, annual consumption has dropped 3.4 percent. Moriarty told the trustees that’s in part due to fewer customers on the system and increased water efficiency by users.

“It doesn’t help us,” she told the trustees. “Our revenue is consumption, so when our consumption goes down, revenue goes down.”

Follow Evan Belanger on Twitter at @evanbelanger.