The Philadelphia Water Department plans to lease another full floor of the Aramark building on East Market Street, as the tower's namesake tenant prepares a move to its new western Center City home.

The utility is increasing its footprint in the 1101 Market St. building, where it already rents four floors, to accommodate staffers from the Water Revenue Bureau call center, which the utility is merging with its now-separate phone center for service calls, spokeswoman Joanne Dahme said in an interview.

Customers have found the existing system, with billing questions and service calls handled by separate units, to be confusing, Dahme said.

The revenue call center staffers are moving to the Water Department's new floor, which encompasses about 23,000 square feet, from the Municipal Services Building near City Hall.

The vacated space at the Municipal Services Building will be used to house 22 employees being hired for a new billing program for low-income customers that goes into effect on July 1, Dahme said.

Aramark, which has anchored the 32-story, 634,000-square-foot East Market Street tower since 1988,  plans to move  next year into a new headquarters building being constructed for the company more than a mile to the west, at 2400 Market St.