OAKLAND — Town sewer customers may see a big increase in the next bill they receive, after the Town Council unanimously approved a 35 percent rate increase this week.

The council also approved a $532,314 Sewer Department budget for 2015-16, a reduction of about 3 percent from the current $549,800 spending plan, at Wednesday’s meeting.

The department, which has a separate budget from that of the rest of the town, has been operating at a loss since the Oakland system was connected to the Waterville sewer system in 2012. In the past three years, it has used about $400,000 of its cash reserve to cover operations, leaving $75,000 remaining.

Town officials have said that rate increase will cover the system’s operating costs and allow it to rebuild its reserve so it can start addressing infiltration and inflow problems that cost the system tens of thousands of dollars a year.

Under the rate increase, the annual user fee will increase from $140 to $200 and the per-unit rate will increase $1.21, to $5.25 per 1,000 cubic feet — about 748 gallons — of water. It is the first sewer rate increase since 2005.

Oakland customers are billed quarterly. According to Finance Director Doug Mather, a customer that uses 11 units of water in the billing period could see their charge go from $79.44 to $109.75 after the rate hike goes into effect.

Most of the system’s roughly 800 customers are residential, and a few are commercial users, Maher said.

Just to break even, the town would have had to raise its rates by 31 percent, Maher told the council at its meeting Wednesday. With the larger rate hike, the Sewer Department will bank about $15,240 to be added to its reserve account.

That money will become important in coming years, as the town moves to tackle the system’s serious infiltration and inflow issues. Storm water gets in through leaks in the system and is pumped with the rest of the town’s sewage to the Waterville Sewerage District for eventual treatment at the Kennebec Sanitary Treatment District. Boyd Snowden, the Oakland Sewer Department superintendent, estimates that 65 percent of all the sewage the town pays to treat is coming from outside the system.

Officials estimate that transporting and treating the excess water adds more than $100,000 to the department’s annual costs.

Until three years ago, Oakland had its own sewage treatment plant, which discharged into an impounded section of Messalonskee Stream. In 2009, the town began construction of a sewer connection to Waterville after it was prohibited by state law from discharging into the stream.

The $6 million project was completed in 2012, and system expenses rose swiftly, from about $375,000 in 2011-2012 to almost $550,000 the next year, partly because it was paying to treat storm water.

The district is working to address the infiltration problem, and Snowden intends to install two system monitoring meters in July to identify leaking areas so repair plans can be made.

Finding and repairing the breaks now could allow the town to reduce rates or delay future increases, Snowden told councilors.

Peter McGuire — 861-9239

pmcguire@centralmaine.com

Twitter: PeteL_McGuire