Lawrence residents may not be able to see the water and sewer pipes beneath the ground, but soon enough the cost to improve their conditions may show up in their monthly utility bills.

City Hall staff members are recommending a 4 percent increase for both water and sewer rates in 2013. City commissioners will consider the recommendations as part of their 2013 budget process, which continues with a study session on Tuesday afternoon.

“I just go back to the situation we have found ourselves in with streets,” City Manager David Corliss said as he explained his recommendation for higher rates. “We did not provide adequate funding for streets and we got way behind. If we don’t have the adequate resources for water and wastewater, we’ll be playing catch-up in that area too, and it won’t be good for anyone.”

How much a 4 percent increase will raise the monthly bills of a household depends on how much water the household uses. But the city calculated for an average household that uses about 8,000 gallons of water per month, the combined water and sewer bill will grow to $72.34, up from $67.78 currently.

Corliss said the rate increases will allow the city to address regulatory issues, maintenance issues, and projects to increase the city’s capacity to accommodate growth. The rates will fund dozens of projects, but three large ones stand out:

• A $54 million sewage treatment plant south of the Wakarusa River. Commissioners in 2007 were on the verge of building an $88 million plant that could treat 7 million gallons of sewage per day, until commissioners ordered a halt to the project as the economy soured and population growth for the city slowed.

Now a recently completed master plan suggests the city can get by with a much smaller 2 million-gallon-per-day plant. But the report says city commissioners need to make a commitment to the project this summer in order to get the plant online by 2018, which is when engineers estimate the city’s lone sewage treatment plant will struggle to keep up with volume and regulatory demands.

If approved, the sewer plant is expected to put upward pressure on sewer rates for years to come. The 2013 rate increase would fund just $5.7 million of the project — mainly for design work. The rest of the $54 million project would be funded in future years.

Corliss said he expects to have significant discussion about the project over the next two months because the stakes are high for the city.

“If you don’t build enough capacity now, you are going to be challenged to build it quick enough when growth starts occurring,” Corliss said. “It might even put us in a situation where we have to inhibit growth, and we don’t want to do that.”

But Corliss also noted other communities — Junction City has been a prominent example — have built expensive infrastructure with the thought growth would come only to be left with more debt than its current population can support.

“But I think we’re being much more realistic about our growth projections than we were back in 2007 when we stopped the plant project,” Corliss said.

• $7.15 million for improvements to the intake pipe at the Kaw Water Treatment Plant. Engineers currently are designing a project to make the main water intake in the Kansas River more reliable. The Kaw Water Treatment plant last summer had to be shut down several times as the pipe was capturing an inadequate amount of water. The city was able to provide enough water to meet the city’s demands through the Clinton Water Treatment Plant, but Corliss said it is critical to have two fully functioning plants.

• $5.64 million to provide a second water supply to North Lawrence. Currently only one pipe crosses the Kansas River to provide water to North Lawrence. If the pipe were to become damaged, North Lawrence could be without drinking water, city officials have said. The city is proposing to build a second pipe across the river near Burcham Park.

Commissioners will meet at 4 p.m. Tuesday at City Hall to conduct a study session on 2013 budget issues. Commissioners are expected to finalize a budget by early August.