Leaky pipes and a growing city may end up costing the average Lawrence homeowner about $500 in extra water and sewer bills over the next five years.

Lawrence city commissioners got the full pitch Tuesday afternoon for why water and sewer rates ought to rise to fix aging pipes and to build a new sewage treatment plant south of the Wakarusa River.

Commissioners didn’t agree to any new rates, but kept the issue of a rate increase alive by asking staff members to bring back additional information in the coming weeks.

“We have some facilities that are just worn out, or out of space,” Mayor Bob Schumm said.

Two large projects stand out in the plan proposed by city staff members: construction of a $54.7 million sewage treatment plant along the Wakarusa River south of Lawrence; and $19.4 million to fix deteriorating sewer pipes.

Work on the second sewage treatment plant would begin immediately in order for the plant to be operational in the next five years. Work on the sewer line project would take place over the next eight years, and the city proposes a host of other maintenance projects.

But commissioners were told Tuesday the projects can’t happen without a significant increase in rates. City officials are estimating the recommended plan will cause the average summer water bill for an average household to increase by about 6.5 percent, or about $4.40 per month.

Staff members, though, told commissioners rate increases will be needed in each of the next five years to pay for the program. The city estimates an average 4,000-gallon-per-month water user would see the average monthly water bill increase by $13.66 per month at the end of the five year period. During the course of the five-year period, the city estimates such a household would pay an extra $453 for water and sewer compared to if the rates did not change.

City staff members told commissioners there were risks if the city didn’t make the improvements, particularly the sewage treatment plant.

City Manager David Corliss said the sewage treatment plant — which would be built just south of the Wakarusa River, roughly across the river from where O’Connell Road dead ends — would meet three important needs: It would give the city greater capacity to handle wet weather storm flows that come through the plant; it would relieve a bottleneck of sewage that accumulates in holding basins and pipes in the 31st Street corridor; and it would give the city more capacity to add homes and businesses in future years.

“If we grow our population by 1.5 percent per year, we believe we’ll be out of capacity by the end of the decade,” Corliss said.

Corliss also told commissioners there was a risk in waiting too long to start work on a new treatment plant because it likely will take five years to design and build the project.

City commissioners were presented with the rate scenarios and service warnings last year, but commissioners thus far have been reluctant to commit to a rate increase.

Commissioners have struggled with the idea of how much the city has been growing. During the last decade, the Census Bureau found the city grew by less than 1 percent per year, but some city planning estimates have contended the growth rate was higher.

On Tuesday, commissioners asked staff members for more information about how much of the projected costs of the proposed plan are related to addressing existing conditions versus those related to accommodating new growth.

Commissioners also will need to decide whether they want to try to add equipment that would address occasional taste and odor issues that arise in the city’s drinking water when algae levels are high at Clinton Lake or the Kansas River.

The necessary equipment– estimated at about $18 million — isn’t included in the staff’s recommended plan. But Corliss said it could easily be added to the plan if a future study shows it would be effective.

But the additions would require additional rate increases. If the taste and odor equipment is added to staff’s recommended plan the total increase in water and sewer bills over a five year period would be about $520 for an average home.

Schumm said he would like the current City Commission to deal with the water and sewer rate issue before the upcoming city elections in April.

“It will be up for debate sometime in March, I believe,” Schumm said.