Water rates for the average homeowner in Naperville are set to increase roughly $5 a month each year for the next four years as the city adjusts to a financial situation that doesn't match projections.

Effective Jan. 1, the average residential customer will owe $75.12 a month for roughly 5,610 gallons of water -- an increase of $4.94 from the $70.18 that would have been owed based on rates approved this spring.

"We regret putting our ratepayers in this situation," said Marcie Schatz, deputy city manager. "The water utility would have been losing money year after year if we didn't put these changes in place."

The Jan. 1 rate increase -- and three others planned for Jan. 1 2019, 2020 and 2021 -- will fill a gap of about $3 million between water utility revenue and expenditures. The gap developed despite a rate study completed late last year by consultant Municipal & Financial Services Group.

Schatz said the study did not account for money lost when water leaks from the system, and it double-counted revenue from connection fees. It also included an estimated cash balance that proved too high, meaning the utility had less in the bank to begin with.

One of the city council's priorities is balanced budgets, city spokeswoman Linda LaCloche said. So the council approved the rate increases to keep utility funds stable.

"This maintains our ability to have safe, reliable water and wastewater services," Schatz said.

Future rate increases for the average homeowner are $5.08 a month in 2019, $5 a month in 2020 and $4.51 a month in 2021. By 2021, the average bill is expected to be $82.14.

The increases leave unchanged a new phosphorus surcharge that went into effect May 1 to save for future improvements at Springbrook Water Reclamation Center. The facility needs to spend roughly $40 million to $60 million to decrease the amount of the mineral phosphorus in treated water to meet a new Illinois Environmental Protection Agency permit requirement.