LOCKPORT — Although the city would have liked to increase its revenue, the Common Council agreed Wednesday to extend the city’s water and sewer rate contract for the Delphi Thermal and Interiors plant for three years without changes.

Mayor Michael W. Tucker said the city wanted to increase the rates, but is aware that Delphi, which is being renamed GM Components Holdings, is financially struggling. General Motors agreed to take back the Lockport plant and some others it spun off a decade ago as part of the settlement of Delphi’s bankruptcy.

“What works for them works for us,” Tucker said. “We have to do what’s fair. Delphi’s trying to get their feet under them. We want that business to be successful.”

Because of Delphi’s large volume of water use and its status as the city’s largest taxpayer, Lockport has negotiated water and sewer rates directly with the plant’s owners rather than using the rate schedule that applies to all other industrial customers.

The extension, which will run through Nov. 4, 2012, keeps the monthly water charge at $15,000. In addition, the city charges Delphi a water usage bill of $1.26 for every 100 cubic feet of water and a sewer usage bill of $2.15 per 100 cubic feet.

In other matters, the Council did not vote on any union contracts. Tucker said only minor tweaks are needed in tentative deals with the police, white-collar and department head unions. They may be on the agenda for the Council’s Nov. 18 meeting.

The Council did vote to spend $130,970 to buy six police vehicles — four marked sedans, an unmarked sedan and a sport utility vehicle. The four patrol cars will come from Howell Motors Ford of Wrights Corners. The gross price of $98,068 was offset by a $13,000 trade-in allowance.

The unmarked car and the SUV will come from Hoselton Fleet of Rochester. The SUV cost $27,767 after an $800 trade-in allowance, and the sedan cost $18,135 after a $700 trade-in.

“We’re trading seven cars in and buying six,” Tucker said.

Also Wednesday, the Council ratified a $170,000, 18-month contract with KLW Municipal of Buffalo to update the city’s property inventory, leading up a citywide revaluation expected in 2011.